In short: It's Batman humour
. There is just nothing funnier than the thought of the big bad grumpy tentacle hoodie monster finding, carrying and protecting a kitten for his baby sister's birthday.
The writer gets more mileage out of the concept than one might expect, including Blackwatch, Randall, Cross, and a few cameos from other game franchises; the world's most punctual and least diligent pet store employee; the recurring idea of kitten grenades; and a truly bizarre method for winning a fight with a Hunter. It's all topped off by a genuinely cute ending, a rare thing in Prototype
fanfiction. It's the very last place you'd look for it, but if you want short, sweet and funny, it's recommended.