Ranma ½ (1989)

S1E158 A Ninja's Dog Is Black and White

Ryoga stumbles upon a black and white dog named Checkers (Shirokuro), who heroically saves P-chan from a waterfall. Grateful, Ryoga decides to care for the pup and provide it with food. In a twist of fate, Checkers snags a love letter Ryoga had penned and delivers it to Akane. Confused by the anonymous note, Akane responds with a letter of her own, expressing her affection for someone else and apologizing for not reciprocating the writer's feelings. Ryoga is devastated upon reading her reply, but when Ranma questions whether he signed the letter, Ryoga realizes she could be referring to him.