Monster Tinder

[Amaterasu]

Strazio Rockwell

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Kunoichi!

As said by Strazio himself, he doesn't have time for romance. And that's fine! Granted, that means that barring the possibility of a monstergirl pulling him away from his revenge mission (which I doubt he would take to very well) most monstergirls can be discarded. Many of them require attention and affection in their daily lives and can become quite demanding if neglected. Well, admittedly Kunoichi will demand a little attention too, but not to the same extent.
Rather, she will prove a valuable ally to have if Strazio can win her over for his cause - and considering how he's handsome and Kunoichis are easily swayed by that sort of thing, that shouldn't be too hard. Once she decides to work for him there's few he could wish for that are as dedicated and loyal as her though: especially because his magic hurts him as well, Kunoichi will want to avoid him using that so that he doesn't get injured. Very anime, I know. She's going to help him as much as she can, and trust me when I say that Kunoichi is among the most combat-trained monsters out there, an expert in assassination, infiltration, deception and open combat if it needs be. Plus, Kunoichis are humans that were transformed into half-succubi by demonic energy, so Strazio doesn't need to adjust to a completely non-human partner.
And while we're on the subject: yes, half-succubus. Kunoichi feeds on the sexual energy of both her targets and her partners, and well... even if Strazio has no time for romance, how about a quick roll in the hay so that Kunoichi can fully charge her reserves before they take on a particularly difficult mission? She might even convince him that he's doing it to further the progression of his goals... until maybe one day, he doesn't need such incentives anymore.
Hopefully with enough time spent together and with Kunoichi becoming more and more invaluable to him, one day he'll acknowledge her as more than a competent sidekick. But even if he doesn't, Kunoichi will be happy with the way things are.