Ritsu Sakuma/Mao Isara is the relationship between Ritsu Sakuma from Knights and Mao Isara from Trickstar.
They're very close childhood friends, and have stayed that way up until their high school years. They live in the same neighborhood, and Mao always has to bring Ritsu to school each day, often go as far to help him change and get ready, too.

Mao is usually the one to carry Ritsu on his back, but in Episode 23 of the Ensemble Stars anime, Ritsu carries Mao on his back, claiming that Mao is "relaxed when he is busy," so he forced him to sleep.

Ritsu often refers to Mao as "my cute, dumb Maa-kun," as Mao has a tendency to be almost comically oblivious to his feelings, leading Ritsu to talk down to him. Mao, on the other hand, accepts this without protest, and his automatic response when Ritsu calls him an idiot is to apologize and offer to kneel to Ritsu if it makes him feel better, even when he doesn't understand why Ritsu is mad in the first place.

In the prologue of the story Band Ensemble, it says that they both met in Elementary School. Mao was told to pick Ritsu up to go to school because Ritsu didn't attend for a while, and Mao kept doing it even years after.

The two have abbreviated forms of Japanese honorifics for each other (san, kun, chan, etc.). Ritsu calls Mao "Maa-kun," while Mao does the same and calls Ritsu "Ricchan." But unlike Ritsu, Mao stopped calling Ritsu by this nickname as they grew older, and just sticks with "Ritsu" when he talks with or about him.