Isshin Kurosaki is the father of Bleach's main hero Ichigo Kurosaki. There is more to this weird doctor than he reveals to everyone else.
In the opening of the series Isshin is seen acting like a child when he attacks Ichigo for being late to dinner. The suprise attack results in Isshin getting beat up by his own sonIchigo. When Isshin and Ichigo begin to argue Yuzu steps in and threatens to not feed either of them if they keep fighting. Isshin then complains about how Ichigo can see spirits but he can't.
After Ichigo leaves the room Isshin also complains that Ichigo never talks to him about his problems with having to deal with spirits. Karin responds by telling Isshin that she understands Ichigo since their father always acts like a child. The rebuff causes Isshin to respond by crying to a mural of his wife he keeps in the house. When Ichigo finds out that his family is attacked by Hollows Isshin is the first to be taken out.
The next day Isshin is there to wake Ichigo up for school dropping on him feet first. After Ichigo is awake Isshin is the first one to get outside and get ready to fix a hole in their wall, cheerfully quipping about how nice it is that no one had died.
On day Ichigo wakes up late for work and wonders where his father is. When Ichigo looks at his watch he realizes that his father Isshin is getting ready for the next day.
Isshin calls a family meeting and discusses the days plans for the morning, where he points out that he had his hair cut despise the unnoticable difference.
When the morning comes Isshin tries to motivate his daughters to continue to climb the sttep hill leading to the cementary that their going to visit. To give his daughters motivation Isshin balances himself on his hands and begins to climb the hill on his hands, picking up speed when Yuzu and Karin ignore him.
Once in the cemetary Isshin and the rest of the family gather at their mother's grave to pay their respects. Isshin is the first to suggest a competion between him and Ichigo in Tombstone Dominos, he stops when Yuzu again threatens not to feed him.
When Ichigo steps in to later stop the Hollow Grand Fisher from eating his sisters Isshin is waiting at the bottom of the hill for his family to arrive. Secrets about this story are revealed later.
While Ichigo is fighting Grand Fisher Isshin keeps Yuzu and Karin in a small temple and notices that there is something different about Ichigo. After Ichigo and Grand Fisher are done fighting Isshin runs into Ichigo at Masaki Kurosaki's grave. Ichigo realizes that Isshin is smoking a cigarette, something he doesn't ever remember seeing his father do. Isshin reveals that he smokes one cigarette each year infront of Masaki's grave.
Before walking away Isshin tells Ichigo that he is proud that his wife sacrifced herself to save their child Ichigo. Ichigo is left standing in the rain at the end of the story almost awestruck as Isshin walks away wishing Ichigo to live a long and fulfilling life.
Isshin is a huge fan of the Don Kanoji's show--Spiritual Hotsprings. He demonstrates his support via watching the show religiously and performing the laughing arm cross gesture, which Don Kanoji does throughout the show.
When the family goes to watch the show, Isshin tries to get on TV like Ichigo, who jumps over the security line. However, he was stopped short by Yuzu. After the appearance of a Hollow spirit, Isshin protects his daughters from the fragmented glass, even though they are distant enough from the window to be safe. Isshin is seen later complimenting Kanoji on his way of dressing himself.
Isshin is only seen once during this story when he and Karin are looking for Chad after his hard-fought battle with a Hollow. After Isshin arrives on the scene and can't find Chad, he thinks that Karin just wants some attention and begins to pester her. Karin shows her dissatisfaction with Issin's actions by attacking him.
Before the four friends and Yuroichi take off to invade the Soul Society, they spend a little time at home at the beginning of their Summer Break. The friends decide to go see the annual fireworks. Sure enough, the rest of the Kurosaki family is there to cause a scene. When the team meets up at the river bank, Isshin shows up and leads them to where he has reserved some seats a lot closer to where the show will be. Isshin also tries to play down the fact that he knowingly drank alchol filled mellons that an old man is always selling.
The last thing Isshin does before his son leaves is to give him a luck/ fertility charm that his mother had. Isshin also tells Ichigo to come back alive. While Ichigo is off trying to save Rukia in the Soul Society, Isshin isn't seen too much.
After the teens have returned home and try to get their lives back in order, everything seems to get worse. While Ichigo is off fighting a Hollow and meeting the new kid, Shinji Hirako, who is also a Vizard, Kon decides to run off in Ichigo's body.
Unbeknownst to Kon, Grand Fisher is back and has come to destroy Ichigo. After escaping temporarily, Kon is eventually caught and saved by Isshin. It is then revealed that Isshin had filled the charm he returned to Ichigo with barriers to protect Kon, should he ever come under attack by any Hollow in Ichigo's body. Isshin explains that he has known, since the time that they visited the cemetery, that Kon sometimes stays in Ichigo's body.
As Isshin approaches Grand Fisher, it is explained that twenty years ago, Isshin has come to the human world and fallen in love with Masaki, who later becomes Isshin's wife and mother to Ichigo, Karin, and Yuzu. It was due to meeting Masaki that Issin has has become a human.
Grand Fisher laughs at Isshin's desire to fight him despite the vast difference in the sizes of their weapons (Fisher's is as big as a skyscraper at this point, while Isshin's is about the size of a regular katana.), and stabs at Isshin, after changing into his final Arrancar form.
Fisher stares in disbelief as Isshin tells him that all captain level Soul Reapers can suppress their power so that their swords are small and not outrageously large like Fisher's. Isshin looks at Kon and explains that he had fought Arrnacar before and then greets Urahara. The two explain to each other that the Arrancar and the Vizards are on the move to achieve their next goals, whatever they may be.
Urahara reveals that Isshin has been in our world for twenty years and has lost most of his powers.
Isshin doesn't display any powers in the story but he was once a captain level Shinigami and actual wears a captain's jacket like a shaw from his left arm. However, there are no markings on the jacket.
Despite his goofy nature in front of his family, he is a surgeon in the real world and is quite knowledgeable in regards to current events in the Soul Society. This knowledge gives evidence to show that he is quite an intellect.
Albeit brief, we witness some of Isshin's swordmanship as he is able to defeat Grand Fisher and his extraordinarily large sword with a normal sized Zanpakutō unreleased.
It is hinted that Isshin has some knowledge about Kido after he admits he placed a protection spell onto an item he gave to Kon whilst he was inside Ichigo's body. This helped protect him against attacks from foes as powerful as an Arrancar.
Aside from his old powers Isshin takes a hell of a beating regularly in the series and walks away without any major damage.
Isshin's Zanpakutō has a shikai, Engetsu, which is a red-hilted katana, and is able to release Getsuga-Tensho. His Bankai is unknown.
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