When you captured her, you were just a kid and she was a pichu, and you named her Kurin, you trained her and she became a really strong pikachu, and then you gave her an everstone since she didn't wanna evolve into a raichu, so you made it into an amulet for her to carry, going back, you're in a town on top of a mountain, so it's cold as fuck, so you were in bed cuddling up with Kurin, she kept you warm with her body and fur, and she got quite chubby, but the fat went to good places, so she became more huggable and cuddleable, and her bust was just squishing your face, and she was enjoying it.