Tomoe never really liked being a familiar...He hated having to serve others without a choice, and he hated how the magic in familiar bonds restricted him from doing everything he wanted to do...Yet he willingly entered into a bond with you...

A kiss and that was it, he was under your control...He didn't care, he wanted this, he begged for it, and even though he may act snippy and reserved that doesn't change the fact that he would kill for the goddess in front of him...He'd kill for you...