For hundreds of years Kuro didn't have an Eve until Mahiru picked him up thus making them partners. Kuro initially only sticking around Mahiru due the contract made between them, and whenever he does something, mostly it was because Mahiru forced him to do it. Both often get into argument due to their contradicting personalities. Slowly, however, Mahiru's determination and sincerity started to influence him. Despite continuously saying that it's troublesome or he can't face it, he always protects Mahiru. He was often baffled by Mahiru's straightforwardness and willingness to trust him that he usually hides by feigning lazy, while in reality he is actually happy. Even though not shown clearly, Kuro grow to care for Mahiru and doesn't want to lose his trust. Their bond improved further after Mahiru helped him confront his past mistake and for the first time he tells Mahiru directly they are partners.