The main protagonist of Tsukihime, he is a caring older brother figure who has been physically weak ever since an 'accident' in his childhood. As events unfold, he is pulled into helping Arcueid Brunestead kill vampires using his Mystic Eyes of Death Perception.
Despite seeming to be Akiha's older brother, Shiki is actually not related by blood to the Tohno family, a clan with demon blood. He was actually born as the elder son to the Nanaya family, a clan of powerful demon-slaying assassins. Shiki winded up being adopted by the Tohnos after his entire family was slain in an attack by the Tohno and Kishima (a family of half-demons) clans. The head of the Tohno clan, Makihisa, chose to spare Shiki since his name was the same as the Tohno's elder son, SHIKI. While adjusting and learning to accept his new family, Shiki would frequently play with Hisui, Akiha, SHIKI and Kohaku.
One day, an incident occurred that would change Shiki's life forever. While playing with Akiha and SHIKI, the latter had given into a demonic inversion that drove him into attacking his sister. Shiki would shield Akiha from the attack at the cost of his life, gaining a large scar on his chest as a result. Makihisa would kill SHIKI, as family traditions required that those who gave fully into their demon blood must be slain. However, both of the Shikis never died that day. Akiha would use half of her life force to save Shiki's life, while SHIKI would instinctively take half of that mentioned life force to save his own life. Because of the events, Shiki would develop both an anemic condition and the Mystic Eyes of Death Perception. Realizing how destructive the latter ability was, Shiki was fortunate to eventually meet Aoko Aozaki, who would give him a pair of magical glasses called Magangoroshi that would seal the effects of his Mystic Eyes for as long as he wore them.
To maintain the image of SHIKI still being alive as the Tohno family was an influential one in the public eye, Makihisa would hypnotize Shiki into believing he was the Tohno family's elder son. He would then send Shiki away to live with distant relatives of the Tohnos in the Arima family under the pretext that Shiki's fragile condition made him unfit to be an heir to the Tohno family and entrusted him with an antique knife, that Shiki is oblivious to the fact it is from the Nanaya clan. Eight years later, Shiki would be called back by Akiha to live with her at her mansion after Makihisa's death.
Shiki stands at 169 cm tall (about 5 and a half feet) having black hair with gray eyes while wearing his glasses and bright blue eyes when revealing his Mystic Eyes. He normally wears the Magagoroshi glasses which seal the effects of his Mystic Eyes of Death Perception.
Normally, Shiki is a fairly ordinary high school student who seeks to cherish every moment of his life due to his close brush with death. He is playful with Akiha and the maids and normally interacts with classmates at school like best friend Arihiko Inui and upperclassman Ciel. However, Shiki can be serious when the situation calls on it and can be flustered or embarrassed. He's known to be a very heavy sleeper as Hisui has trouble waking him in the morning. In addition, he seeks to get a job for himself as he doesn't want to live on weekly allowances given to him by Akiha.
Suppressed in Shiki's conscious is a darker side to him that possesses the skills and instincts of his Nanaya family blood. This side of Shiki manifests when in contact with any demonic threat, having a cold personality with the desire to kill any enemy that approaches him. He will acknowledge enemy threats with curt remarks or a lethal stare. Shiki refers to his Nanaya side as "him" and another person.
Note: With exception to Arcueid's route, all routes listed here are from the Tsukihime visual novel.
Arcueid is killed on sight by Shiki upon their first encounter with one another when the boy slices her up 16 times by cutting her lines of death with his Mystic Eyes of Death Perception. This was a result of Shiki's Nanaya blood reacting instinctively to her. Upon realizing what he has done, Shiki would flee the scene of the slaughter.
The next day, Arcueid would meet with Shiki after he gets out of school and scares the boy into fleeing until she traps him in the dead end of an alleyway. While the two converse, they are attacked by one of Nrvnqsr Chaos' beasts and find themselves teaming up against the Dead Apostle since Arcueid's power is not at sufficient strength yet for her to fight alone. Shiki manages to kill Chaos by striking one of his lines of death using his Mystic Eyes. The two then decide to continue their partnership to track down Roa.
As the story progresses, Arcueid and Shiki come to understand one another as Shiki shows Arcueid various things of the modern era that she didn't consider important, such as movies. She attempts to bite Shiki at several points, but resists the impulse on time and usually finds herself having to run away from Shiki until her impulses settle down. The two eventually fall in love with one another despite Arcueid's vampire lineage and slight instability, enough so where the two have sex with each other.
Discovering that Arcueid had sneaked off to confront Roa, Shiki flees to the school in time to see Roa appearing to kill her. Distraught at the sight of his lover being killed, an enraged Shiki uses his Mystic Eyes to destroy the walkway both he and Roa are on as a distraction to cut apart Roa's point of death. Being killed in this way nullifies Roa's very existence and would prevent him from ever reincarnating again in the future.
Later on, Shiki comes to see that Arcueid is still alive in his classroom and having regained the power that Roa stole from her. However, she could no longer restrain her vampire impulses and decided that she would go into an eternal sleep where she would always dream about Shiki. When Shiki offers to have Arcueid suck on his blood, she turns down the offer saying that she would always love him.
There are two different endings shown in the visual novel and manga with Arcueid. In the visual novel, there's a "good" ending showing Arcueid resisting her vampire impulses for a week and goes off to meet Shiki at the same place he had killed her where the two would spend the day together. In the manga, Shiki would go on a journey to track down Arcueid after she said her farewells to him and they would reunite together.
When Ciel and Shiki work together in killing Roa as SHIKI Tohno, he manages to transfer his soul into Shiki before his demise. This results in Shiki losing control over himself as he develops murderous thoughts and strange dreams, one of which where he witnesses the bloody slaughter inflicted by Roa while he possessed Ciel's body. After brutally attacking and raping Kohaku from his lack of control, Shiki flees from the Tohno mansion and seeks out Ciel's help, afraid to be in contact with other people out of fear for what he would do to them.
The two meet on the roof of the school where Ciel is armed with the Seventh Holy Scripture. She then tries to kill Shiki, believing that death was the only means Shiki had to free himself from Roa's madness. However the love she developed for the boy leads her to lack the desire to kill him after immobilizing the boy, as she collapsed in the boy's arms and cried. The two then go to Ciel's apartment where Shiki's body becomes excited from Roa transferring into his body. Realizing this, Ciel devises a means to calm Shiki's soul through intercourse. However, this only strengthens Roa's control over Shiki, as the boy flees from Ciel's apartment and encounters Arcueid. Having come to kill Shiki with Roa possessing his body, Arcueid blames Ciel for his current condition and offers to help him if he obeys her. Arcueid's actions will depend on what choice you make for the situation in the game.
If you agree to Arcueid's conditions, this triggers Ciel's "Good Ending". Arcueid will proceed to kiss Shiki and tempt him to bite her neck and drink his blood. Ciel stops this from happening and the two argue over what the best means would be to rid Shiki's body of Roa. As the two argue, Roa gains control over Shiki's body and the boy tries killing himself by slashing his chest with a knife to stop Roa. The boy then has a vision of Roa's past before he became a Dead Apostle and Roa finally vanishes for good. With Roa defeated, Ciel and Arcueid decide to "share" Shiki, triggering a sort of harem ending.
If you refuse Arcueid's conditions, this triggers Ciel's "True Ending". Arcueid will become angered by Shiki's refusal and this leads Shiki to slash the line of death in her neck using his Mystic Eyes of Death Perception. The attack drives Arcueid into a murderous rage as Ciel arrives in the nick of time to flee with Shiki to the school. Ciel tries to fend off Arcueid when the True Ancestor arrives, yet is easily defeated. When Roa's control of Shiki's body intensifies, he attempts to kill himself by slashing his throat to calm Arcueid and kill off Roa. This action leads Arcueid to return to her normal state and vanishes as she bids farewell to Shiki. Shiki managed to survive his attempted suicide as Ciel takes him back to his house to treat his wounds and the two become a couple.
Regardless of the ending though, Shiki's efforts lead to the end of Roa's reincarnations and restore Ciel's mortality.
Upon moving in with Akiha, Shiki finds himself dealing with her cold and distant persona as she tries conforming him to a strict lifestyle befitting of the Tohno family heir. He assumes that Akiha bears a grudge on him for the eight years they were apart.
When he comes to learn of his classmate Satsuki being turned into a vampire, Shiki would confront her on two different occasions where he would be wounded in both and succeeds in killing Satsuki in their second encounter. Both incidents would lead to Akiha reprimanding Shiki for arriving back to the mansion late and treating his wounds.
Akiha later starts spending more time with Shiki by becoming a student at his school. A recent string of murders leads Shiki to later suspect that Akiha may be involved with them until he encounter SHIKI at the family mansion with an unconscious Akiha. SHIKI reveals that he has come to take Akiha "back with him" and reveals their past together. She would eventually awaken and protect Shiki. Upon hearing from Akiha that she no longer acknowledges him as her brother. an enraged SHIKI goes in to kill Shiki until Akiha steps in to take the attack. This event triggers Shiki's Nanaya blood leading him to cut SHIKI's lines of death with the Mystic Eyes of Death Perception.
Afterward, Shiki and Akiha would talk in the latter's room where she reveals the true events of his past. As Akiha starts having spasms and her hair turns red, she reveals that she was aware of not being related to Shiki yet retained the facade because she wanted to be with him. Shiki acknowledges that he sees Akiha as both his sister and a woman, leading the two to kiss and have sex. Following the events, SHIKI would arrive in a jealous rage and abduct Akiha.
Later arriving in the hidden room where SHIKI had been imprisoned, Shiki discovers that SHIKI had turned Akiha into a mindless monster and apparently raped her. The two would fight, with Shiki getting the upper hand yet hesitant to kill his former friend. SHIKI would vanish and return to Akiha's location where he is killed by her after she rips his heart out. You are then given three choices for how to deal with Akiha.
If you choose to kill her (which Akiha wanted in case she became a monster), this triggers a bad end.
If you spare her, this trigger's Akiha's "Normal End". Here, Shiki would regularly visit the monstrous Akiha in the hidden room to allow her to painfully suck his blood to contain her bloodlust, hoping that she will one day be herself again.
If you choose to kill yourself, this triggers Akiha's "True End". With Shiki's death, Akiha regains the portion of her life force she gave to him which restores her sanity and gives her the strength to control her demonic blood. Later returning to where he died, Akiha sees Shiki's knife and touches it. Sensing a faint heart beat from deep inside the knife, she sees this as a sign that Shiki is still alive and holds onto the hope that he will someday return.
Returning to the Tohno mansion after eight years, Shiki recalls the times where he played with Hisui and Kohaku as children, with one of them being a quiet girl who gave him a ribbon. However, he mixes the two up as he believed Hisui to be the mentioned quiet girl. She used to have a more cheerful and outgoing personality, yet took on a more subdued personality for Kohaku's sake from her traumatic experience with Makihisa.
At Shiki's welcome party, Hisui would pass out after drinking a glass of wine due to being unaccustomed to drinking. Shiki would carry her to his room to rest and would also fall asleep, dreaming about the girl who gave him the ribbon. The following morning, Shiki sees Hisui sleeping on his chest. As the route progresses, Hisui grows more comfortable around Shiki and reveals more of her true personality to him, yet doesn't reveal Kohaku's plans to destroy the Tohno family.
After SHIKI Tohno drains Shiki of his life energy, Hisui offers to Synchronize with the latter to defeat SHIKI. After this, she would start to accompany Shiki to school.
In Hisui's "True End", Kohaku reveals that she killed Akiha and SHIKI and commits suicide. Before dying, she reflects that she has no regrets for her actions as they helped to save Hisui from Makihisa. Hisui would begin a relationship with Shiki and accompany him on his vacations, throwing her sister's ribbon into the sky before leaving with him.
In Hisui's "Good End", Kohaku reveals her involvement in the Tohno family's downfall and claims to hate Shiki for their silent connection together. Hisui appears and reveals that her sister is lying as she loved Shiki and Akiha. If Kohaku truly wanted to take on Hisui's personality, then loving Shiki is an integral part of Hisui's personality. Hearing these words, Kohaku attempts to kill herself with poison yet is saved in time by Shiki. She loses her memory afterward and is renamed "Nanaya" by Hisui, as she returns to being a maid at the Tohno mansion. Later on, Shiki and Hisui would go to Hisui's favorite spot in the city together.
Regardless of the ending, Hisui would regain her cheerful personality.
Events with Kohaku at the start of her route play out similarly to Hisui's. However at the welcome party, Shiki goes outside to cool down from drinking when he meets Kohaku. He tells her about the quiet girl from his past and Kohaku warns him that he will face suffering for so long as he stays at the Tohno mansion. Noticing that Shiki is becoming intrigued about his past, Akiha locates and slays SHIKI before her brother can dream about him with Kohaku's help.
Shiki later learns that Kohaku was the girl who gave him the ribbon and that Akiha has given into bloodlust due to gaining SHIKI's burden of madness. Kohaku believes that Shiki reciprocating Akiha's feelings for him is the only way to calm her. Shiki refuses to do this because of his love for Kohaku and returns the ribbon to her. This leads Kohaku to cry and give up on her plans of revenge on the Tohno family. The two have sex and Kohaku offers to Synchronize with Shiki to give him the power needed to stop Akiha. Instead, she attempts to put Shiki to sleep with a sedative so she can confront Akiha alone. However, Shiki is able to resist the drug's effects.
At the school, Shiki confronts Akiha, who acknowledges the suffering that her family put Kohaku through and still assumes that the maid is out for revenge on the Tohno family. Shiki reveals that he still loves Kohaku, driving Akiha to attack the latter with her hair. These events lead Shiki to try attacking her, yet he can't bring himself to kill Akiha. Kohaku appears unharmed and reveals she no longer bares hatred for the Tohno family, with Akiha revealing that she held back in inflicting any harm on the maid.
In Kohaku's only ending, she forgives the Tohno family and goes on vacations with Shiki in the Nanaya forest.
Shiki's Nanaya bloodline gives him physical feats comparable to an Olympic-level athlete, despite his seemingly frail body. He is capable of two skills that are a demonstration of his great speed and used to follow up into other attacks: the Sensa (Flash Sheath) and Senso (Flash Run). Sensa allows him to attack extraordinarily quickly and Senso lets him move quickly enough where his foe loses track of his movements. Shiki is mainly an instinctive fighter, as he makes use of the subconscious knowledge of assassination techniques from the Nanaya family to perform attacks with his knife, the Nanatsu-Yoru. He also possesses a high level of endurance and is capable of surviving near-death blows. Shiki's Nanaya personality will manifest whenever he is in a life-threatening situation or dealing with a demonic threat.
As a result of his near death experience from childhood, Shiki gained the Mystic Eyes of Death Perception, that allow him to perceive the fated destruction of any object or living being in the form of lines and dots. Cutting the lines of a target in this way will damage a part of their form and prevent regeneration from healing them, outright ignoring any defense when attacked in this way. Cutting dots will lead to the target's concept being destroyed meaning a living target will be instantaneously killed and being incapable of revival or reincarnation. Shiki's Mystic Eyes are always active thus he requires the Magangoroshi glasses to seal their effects when he isn't in combat. This is vital as prolonged use of the Mystic Eyes would take a toll on Shiki's brain and trying to comprehend death from more unique existences like Heroic Spirits and True Ancestors run the risk of overloading his brain to the point where it would eventually kill him.