ナンダバ・ナオ太 (Naota Nandaba)

A young elementary schooler, fixated on the idea of acting mature. He's usually pretty cynical and bitter, though can be a bit smug at times. Bored with his life, dissatisfied with the people around him, and stuck in puberty and self-discovery, he's got a lot on his plate. While he idolizes his older brother, Tasuku, he's also been forced to live in his shadow, even taking up his old ex-girlfriend. Ultimately, all Naota wants is to be content with his life, and for people to appreciate him for who he is.

ハルハラ・ハル子 (Haruko Haruhara)

The catalyst for Mabase's newfound chaos, Haruko is a loud-mouthed, Vespa-driving, Rickenbacker-wielding sociopath. Showing up for seemingly no reason other than to stalk and bother Naota, her motives are as mysterious as they are unhinged. She's rarely ever serious, is quick to muddy her words with puns and pop-culture references, and can come off as pretty arrogant. Despite her unconventional personality and unclear goals, she still carries a genuine care for Naota, and is a pretty competent fighter too.

サメジマ・マミ美 (Mamimi Samejima)

The ex-girlfriend of Naota's older brother, Mamimi is a simple delinquent, often spending her days skipping school, and playing videogames by the riverside. She also has an interest in photography, usually carrying around a camera. She often comes off as ditzy, and in her own little world. In a way, she is. Broken up by Tasuku moving away, her attachment shifts to Naota, entering into an almost-sort-of relationship with him. He's just a surrogate though, one of many that Mamimi uses to qwell her lasting obsession.

カンチ (Canti)

The unsung badass of the show, Canti is a rogue Medical Mechanica robot, and usually the one to kick ass at the end of every episode. He doesn't speak, though his mannerisms show him to be very polite and friendly, happily helping around Naota's house. He's also a bit shy, and is easily flustered. He has the ability to swallow and absorb Naota, powering himself up in a reddened state to fight whatever's in his way. He's also constantly being targeted by other Medical Mechanica robots, seemingly sent after him. No one seems to know why, though...