Aww. I took in Lilly as Koda was a jerk towards his sister Miez. I figured he needed a new playmate. Lilly was a kitten with anxiety issues. She kept hiding in her box that she was gnawing apart until there was nothing left, which was a huge improvement as she had an open wound from knibbling on her hind leg.

She was just afraid of everything. I started introducing her to the others by letting her hide in the living room table instead. Koda was definitely her motivation to come out, as he simply would not react at all to her hissing at him when he went past her. They started playing together until she had so much muscle that she almost reached his weight, just half a kg apart, which is quite impressive as he is a real big boy (partially maine coon):

They now live with friends of mine: