She later becomes one of his main partners for Heart Hybrid and by the end of the series, he is having sex with her very often.
Despite being blood related and 10 years younger, Kizuna admits that he's sexually attracted to her. Age-Gap Romance: With his sister, Reiri, who's his parental surrogate and technically old enough to be his aunt.But on the other hand, the anime also gave him the ability to draw on the power of the girls without Climax Hybrid by sheer Power of Love, something he never did in the light novel. It also didn't show him getting a good hit on Zelshione with nothing but his Determinator credentials. On one hand, the anime removed Kizuna's fight with a Brainwashed and Crazy Yurishia, where Kizuna took the Super Speed he got by copying Aine's Zeros and elevated it to a level where he is basically moving at the speed of light. Adaptational Wimp: Zigzagged in the last episode of the anime adaptation.Accidental Pervert: Thanks to his sister.If the partner has a HHG of the 'Ros' series, they will also gain access to their Immoral Weapons.
If he also achieves Climax Hybrid Kizunas Eros temporally copies the abilities of the HHG of his partner. His primary function is to perform Heart Hybrid with his teammates to restore their Hybrid Count. However since men have a low compatibility with HHG, his armor has low offensive capabilities. He was implanted with the first Heart Hybrid Gear (HHG) core called 'Eros' as a child in an experiment conducted by his mother. True Companions: Aine, Hayura and Yurishia werent very close when first introduced, but thanks to Kizunas arrival, Amaterasu fully becomes a united team.It's later confirmed that she comes from another dimension. Multinational Team: Kizuna and Hayuru are Japanese, Yurishia is American, Silvia is British, Aine is unknown due to her Mysterious Past.This one puts them on the same level as a Physical God.
At the end of the series the cast discover the Ecstasy Hybrid, which requires them to actually have sex. It gives each HHG a massive surge in power and unlocks their hidden "Immoral Weapon". Climax Hybrid is the next stage, requering much more sexual acts. Heart Hybrid is essentially foreplay which is done to heal the HHGs and restore their energy levels.