Now, why bother doing that with pets well-behaved enough to not merit squashing when rape-victim-kos are free for the taking and have probably endured enough suffering - *just from their mother's misdirected hatred* - to be miles more delicious?
Maybe they're all livestock. They're not trash, but that doesn't mean they're pets. Perhaps he just picked Reimu up, and decided to sample 3 of the babies and is leaving the rest to mature. And it was too stupid/done stealthily so Reimu didn't notice. The other ones are Alices... typical rape breed...