Rin Shiragiku is a member of the White Knights often seen with Kana Shiraishi. While they seem to be best of friends, she doesn't doubt to abandon Kana when Aika Sumeragi shot though Kana's shield, which was protecting them both.
Like Kana she has Alien Tendrils in her body that she uses as weapons.
Rin has a slim body and an average height at around 5' 4" with both green hair and eyes. Her most distinctive feature are her particularly huge boobs, especially taken into consideration her young age. She boasts the biggest breasts out of all the White Knights, with the possible exception of E.T.A.I. who is however much bigger in overall size.
Rin first appears at the end of episode 1 where Yui, Misaki and Nanami are unconscious after Aika defeats them, Reiko, Manami and Misumi give them to the tendrils.
In episide 2 those three are knocked out, Misumi is already on the couch so Rin has to carry Reiko's cody over to the same couch, then Kana and Rin bend over and are knocked out themselves
Near the end of Episode 3, Rin fights Aika together with Kana. After the later is defeated, she still tries to take her on by herself. They clash for some seconds, until a flying kick by Rin ends with Aika getting a hold of her legs and throwing her violently against a wall, which she hits head first. Her body then slumps down and falls to the floor, defeated. Though apparently left out of comission by the blow, Rin remains conscious after the impact and Aika graciously pardons her in exchange for information on the location of the missing girls.
Despite this act of mercy, Rin still attempts to launch a sneak attack on Aika as soon as the salvager turns her back on the seemingly surrendered high school student. While the victorious girl is calmly walking away, the White Knight makes it evident she is not all that affected from the fight, revealing a hidden blade made from alien tendrils and quickly going after Aika with the intention of stabbing her in the back.
However, Aika seems to already have been expecting such a cheap and deceitful tactic, and dodges the move easily by jumping above the girl just as she comes barging in. The evasive manouver totally startles the over confident Rin, who stops right on her tracks as she worringly comes to the realization she has lost sight of the Salvager, who disappears above her. The girl then desperately starts trying to locate her foe before it's too late, but by the time she's only just beginning to look upwards to try to find her, Aika is already quietly landing right behind the unsuspecting student. Aika lands behind Rin with a soft thud garnering Rin’s attention. While only moments pass, Rin’s facial expressions display a dramatic chance of emotions. First, Rin realizes Aika is behind her, this is followed by slight worrie as she realizes she has been out maneuvered. Next comes an expression of horror and regret as she sees Aika straightening up her hand in preparation to land a devastating blow to the poor girl’s neck. Fully realizing she had no time to formulate any kind of counter move, Rin’s face fills with worry and regret likely contemplating her decision in lite of Aika originally sparing her. Aika’s face on the other hand if covered in a look of annoyance and frustration with the high school student due to Rin’s shameful and ultimately pathetic attempt to exploit her compassion for the then seemingly defeated White Knight. Rin appears to understand and regret her decision but it is too late realizing Aika’s frustration and determination to finish her off. Rin doesn’t have time to do anything other than gasp in shock as Aika finally drivers a brutal neck chop of retribution to her neck leaving her out of commission for good. A loud and forced Yelp comes from Rin as Aika’s blow lands causing her face to gush out saliva all over the place, her face contorting in an expression of extreme pain and anguish. Her face goes blank as she absorbs the devastating blow. Expressionless, she makes a few more gasps as her eyes roll into the back of her head. A few off camera noises are made as she appears to attempt to breath. Rin then falls to the ground face down with a sad yelp, her butt bouncing as it hits the floor, lifting her skirt and exposing her panties. She then lies there motionless in a fairly unladylike position as Aika looks over her motionless body in frustration; seeming not having even the slightest remorse for the White Knight.
Due to her high level among the White Knights, once she is out could her butt is used as a password to get to Miyu Shiratori and E.T.A.I. To this end, Risako drapes the unconscious body of the defeated girl over her shoulder and then presses Rin's ass against the closed door. The woman even goes as far as first spreading Rin's legs in order to get a better contact surface between her butt and the door, camera obsiously ready to get a great frontal shot when she does, in what represents a fairly humilliating and probably unnecessary gesture with the beaten foe.
Rin's unconscious body is later retrieved and draped over a metal slab along with the other White Knights after there's no further use for it. She and Kana both wake up for a few seconds, only to be hastily put down again by Karen with two well aimed shots to each of their butts. Upon impact, the helpless girls arch their backs and raise their butts for a moment, while letting out two barely audible screams, before collapsing once more, their mouths drooling.
Rin shares with Kana the dubious honor of being the girls knocked out the most times on screen of the entire Aika franchise, a total of 4 times each. However, rather curiously, it only happens one time at Aika's hands. The first two they are left unconscious by Miyu Shiratori and E.T.A.I. with alien tendrils, initially to get them into the White Knights and later "for insurance", much to both girl's surprise when it happens. The third time is when they do face Aika in combat, and finally the last occasion is when, already defeated, Karen thinks they still deserve some punishment for their actions and hastily puts them down again with tranquilizer darts to their butts just as they begin to regain consciousness.