Ranma ½ Part 5 number 1

The story starts with Ukyo confronting Genma. She beats him up and sends a challenge to Ranma on an okonomiyaki. Akane thinks Ukyo is one of Genma's kids. Ukyo enrolls at the same school and Ranma finally remembers who she is.

They were childhood playmates until Genma pulled one of his stunts and separated them. (I like the Ranma ½ fiction stories where Genma finally gets what's coming to him for his abuse of Ranma for years.)

Ranma, though, thinks Ukyo is a boy. Ranma pretty easily gets the best of Ukyo, sending him out of the ring and running right after him. Ranma grabs on to Ukyo and then realizes that what he has grabbed are her breasts. (Just like what happened to Ranma when he and Kuno fell into the pool and Ranma changed to Ranma-chan and Kuno grabbed her breasts.)