The Kappe Alien mission was Reika's first mission as a Gantz hunter thus she did not know a thing about the situation at hand. Kei, one of the the most senior, made a point to let her and others know what was going to happen. Most didnt listen but Reika gave her full atention and put on one of the suits. This proved lifesaving as Reika was nearly torn to shreds by two dinosaurs.
As advised by Kurono during the very start of the mission, Reika basically sat around watching Kei fight for the most part doing nothing pivotal to completing the mission. Reika attempted to give some support to Kurono and fight at one point in the mission as they were surrounded by aliens. Kurono denied her though, seeing that her suit had failed he
Oni Alien

Reika killing off a group of aliens by herself
Surprisingly enough, Reika the idol proved to be a formidable opponent against the Oni Aliens. Strong, brave and quick on her toes, she proved that she was a valuable part of the team even showing that she had leadership skills when she commanded a group of fighters when she and Kurono decided to split up. She had also shown skill in fighting as she fought and defeated a group of aliens that surrounded her by herself.
Reika is concerned to find a young boy named Takeshi has come into the Gantz Room. Reika and Yoshi strive to get the boy into a suit before the transfer begins. Takeshi just stares at Kaze. The transfer begins as the team must hunt down the Oni Alien Boss. Reika immediately approaches Kaze and asks him to get the suit on the boy.

Reika leading Gantz fighters
Under the orders of Kurono, Reika leads Nagashima and his friends. She tries to explain how to use the guns. Nagashima and his crew are too busy thinking if she is really Reika the model. Reika gives up and just goes into a mall as the groupies follow. They find the alien in the human form. The alien reveals having knowledge of Reika and the hunters. The alien transforms and startles people to reveal they can now be seen. Reika is the only one to avoid a flurry of tentacles. She fires on the aliens but it dont die. Reika follows the surviving alien only to end up being ambushed. She finds the aliens can talk and are able to track all the hunters in the area. The aliens are mad with the Gantz hunters for killing their kind. She tries to explain being forced into the mission but the aliens dont care and were actually deliberating on whether she is the real Reika and if they should rape her. The aliens were all killed by Reika though by herself, showing great skill and courage
Reika gathers the remaining new hunters and searches the mall. She is disgusted to find Inaba making out with the Metaphor Oni posing as her. Reika fires but the oni is too fast to hit. She frees Inaba but the Metamorph Oni escapes once again. She finds Kurono and they return to the others to devise a plan against the aliens. Inaba questions if Kurono was real or not. He isnt and everyone fires. The alien turns into Takeshi and goes inside a hunter's body to kill him from the inside.
The Metaphor Oni goes on a rampage as an elephant only to be killed by the real Kei. Matters grow worse after Kenzo and Kaze have each killed alien leaders as well. The boss calls out the hunters for a showdown and plans to kill humans if they dont come soon to face him. Reika and others prepare to go fight only to encounter Hikawa and his Vampires. The Vampires just pass on by without a word.

Kurono rescuing Reika
Everyone comes to find Shion fighting the Boss Oni by himself and losing. During the fierce battle it gets to where Reika is amazingly the last one standing. She is grabbed by the alien before being able to lock on to him. When the alien seems to have finally decided to kill off Reika, Kurono literally falls from the sky, saves her and begins to duel the alien. Shion returns as well and together with Kei they kill the Boss Oni Alien, ending the mission.
Reika returns to the room with others that weren't seriously hurt. She waits with Kei and Takeshi for the others that were near death. All the veterans except for Hiroto return. Reika ends up with 102 points for the group of aliens she killed. She decides to revive Tae for Kurono. Reika is forced to bid farwell to Kei as he uses his points to be freed of Gantz. She confesses her love for him as Kei vanishes and his memories soon to be erased.
At one point of the manga, she uses her points to resurrect Tae after she was killed in one of the missions because she wants Kurono to be happy. It is not until Kurono chooses to be free that she confesses her love to him. After Kurono departs from the game, she is appointed the new team leader of Gantz. After Kurono is revived, Reika confesses her feelings to him, but Kurono, having rekindled his relationship with Tae, rebuffs her. Distraught over Kurono's choice, Reika suffers an apparent mental break, and resolves to earn 100 points to revive a new Kurono for herself. She succeeds in reviving a second Kurono who exists concurrently with the copy brought back straight from the Oni mission end transfer.

Kurono Clone and Reika in the bath tub
The second Kurono now lives with Reika and she seems that she has decided to quit her job to be with him. At first, he pushes away Reika’s hits but, at night, not sure what really caused it, Kurono decides to "rape" Reika for a few moments. Not sure if he did it more out of hate, and when he saw Reika was okay with it, he lost that taste and didn’t want to do it anymore. After a while though, Kurono starts softening up to Reika and she, in turn, fall for him even more even going as far as suggesting as to changing her name to Reika Kurono.
The morning after, Kurono clone coincidently meets the original Kurono. The clone ends up telling the real Kurono all about how Reika cloned him. The real Kurono, though, doesn’t really see the problem, as Kurono is with Tae. Kurono clone gets frustrated at himself and how he sometimes act. But despite all this, he ends up accepting it anyway
The End is nigh
Currently she and her Kurono have met up with the Gantz Tokyo team and have recruited some other fighters from other teams all around Japan. Kurono made an announcement to all the Gantz fighters alive suggesting that they all collaborate and fight against the alien threat. At first no one responded to Kurono's announcement until he let Reika ask for help. Several answered the call, though their true intention remains unclear until now.
The team, led by Kurono and Reika, is trying to stop the alien invasion by invading the alien ship and finding its weak spot.
Personality and Fighting Style
Reika is a kind person showing compassion for those killed during the Gantz missions. She is best described as Kurono's "side kick" during the missions, providing support for those trying to stay alive and helping Kurono complete his missions. Unlike most of the other Gantz players, Reika is quick to charge at the aliens if it means helping Kurono.
Despite her supermodel looks and her kind disposition she is a very strong woman on the inside. She is vigilant and prudent with her decisions, especially when her decisions directly affect her, Kurono, or her teammates. Although she can be intimidated at times, she can also show great courage as seen during the team's battle with the aliens
Trivia 
- In the anime, posters of Reika are seen in Kurono's bedroom.
- At the start of the anime series, Kurono picks up a magazine before going to the subway where he dies, looking it over, and there is Reika on the cover. In the original manga, a model named Ayato Kajimoto was used.
- Several Gantz manga chapters have Reika on the cover, she is mostly seen in various revealing clothes often related with the Gantz suits.
- In the Oni mission , several of the aliens recognized her, and stated they were fans.
- Reika never appeared in the anime