Nene to Ikoku no Mahoutsukai: Isekai ni Shoukansareta to Omottara, Naze ka Koneko to shite Aigansaretemasu

"I'll give you all the magic you need, my cute kitten." One day Nene is summoned to another world to be a familiar for Kyle, the founder of all sorcerers and architect of the magic tower. Kyle tells Nene her body fused with a cat during the accident when she was summoned. Nene can't hide her shock at the ears and tail that have sprouted from her body, and now Kyle's words truly hit her. If nothing is done, she'll turn into a cat. In order for that not to happen, Kyle has to replenish Nene with mana. But to do that, they have to have sex?! Two people from different worlds, yet they coexist with one another... (Source: MangaPlaza)