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 green hair and particularly big boobs, especially for her age.
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 acheap and deceitful tactics, and dodges the move easily by jumping above the charging girl. She then lands quietly right behind Rin, as the surprised girl stil tries to find out what went wrong. The White knight barely has time to realize where Aika has gone before a brutal neck chop hits her, leaving her out of comission for good with a loud moan. She then falls to the ground with a sigh, her butt bouncing as it hits the floor. Due to her high level among the White Knights, her butt is later used as a password to get to Miyu Shiratori and E.T.A.I.
Rin's unconscious body is later taken and draped over a metal slab along with the other White Knights. 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.