Mutsumi (called Saburo in the anime, Hojo in the manga) is Natsumi's classmate—a poet, artist, and part-time philosopher who'd rather skip class than attend it. He runs his own radio show that Natsumi actually listens to, which probably says something about her taste in entertainment.
His real claim to fame is his partnership with Sergeant Major Kururu, a Keronian who handed him a magical pen capable of bringing drawings to life. The two bonded after Kururu went rogue trying to turn their school into his personal servant army, but they clicked immediately—same wavelength, same weird energy.
Intellectually speaking, Mutsumi's in rare company. He scored a perfect 300 on an IQ test and excels at basically every sport, which makes him something of an outcast among his male classmates who don't quite know what to do with him. Despite being genuinely clever and observant about most things, he's completely oblivious to Natsumi's crush on him—though Giroro certainly isn't, and he makes sure Mutsumi knows it by pushing him away whenever they get too close.
He's popped up in a few episodes of Seven of Seven as well. His nickname is based on Japanese number wordplay, if you're into that sort of thing.
Content compiled by AnimeList.moe from publicly available sources.
