Pochi to Goshujinsama♥

Hiro has always seen his childhood friend Chiwa as a little sister. Instead of a promise to marry, they once made a pact with a toy choker to maintain a relationship like a dog and its master. When Chiwa moved to England with her mother, she vowed to return to Japan one day and be in the same class as Hiro.

Years later, Chiwa learns that her mother is about to remarry Hiro's father. If she becomes his true stepsister, she fears she can never marry him. Hurrying back to Japan, she asks Hiro if he remembers their childhood promise. She offers to become his pet, hoping he will love her deeply.