I have a feeling this is just behaviour or heat-related. Where should I start though, a general consultation or bloodwork or something else?
Yuki hasn't been under an kind of stress, I've been away for a week before and my neighbour never noticed anything unusual (they own cats too*).
(And never pick up my other cats by the scruff of the neck, it's just that Molly weights about 4lbs. and I raise her just enough to get my hand under her back feet. She's instantly playful if you touch her belly and brings out the claws and teeth)
*You should see their kitchen-table cat, he's going blind but he has the biggest eyes I've ever seen, they're practically googlie and he's such a sweetie.