Any good anime or manga of a animal(or fictional one) that is transformed into a human. I know of three anime examples,
Girl's Bravo episode 9.
https://i.imgur.com/tAkmjGK.png
https://imgur.com/a/GYNNDdP (Hard finding a good snapshot)
Ebi a seal like creature is turned into a young girl by transformation magic. Not turned back at episode's end but reappears as her original self in later episodes.
Haiyore! Nyaruko-san - Season 2 - episode 8
https://i.imgur.com/71dvlD3.png
https://i.imgur.com/Vs21Liy.png
Similar to Girl's Bravo Shanta the pet of the main characters is given "strange candy" that turns her into a preteen girl. At the end of the episode her transformation wears off.
Conception episode 12
https://i.imgur.com/TOJIIGo.png
https://i.imgur.com/ubKb4Bs.png
https://i.imgur.com/eFEGp69.png
https://i.imgur.com/9n0LNHP.png
Mana a fairy/panda creature with a partially perverted personality(who is quite taken with the male lead) is reborn as a teen girl at the end of the anime when the male lead returns to his world(along with the rest of his harem). Interestingly the character has a route on the game the anime is based on. At the end of her route she becomes human and enjoys a normal school life with the male lead after returning to his world.
I heard of the animal characters in the Jewelpet series gaining human forms.
I recalled a romance manga of a dog that is transformed into a teen girl though I can no longer remember the name of the manga.