Sumai is one of the employees at ASAGI. Tech Corporation, and also one of the 4 major 'villains' of said company.

Known for being spontaneous, erratic, and quirky, Sumai has been known to be an incredibly peculiar individual to work with. Her odd behaviour and inconclusive history have led some people to spread rumours about her, much to the dismay of Itami. Sumai doesn't mind the secret gossip about her. If anything, he enjoys the fact that more people know that she's around...to some extent.

Itami often assigns Sumai to work alongside Mei during her ploys, much to Mei's annoyance. Chi is also an unfortunate victim of Sumai's regularly pestering. While she derives enjoyment from fooling around and teasing the two every now and then, she genuinely appreciates the acknowledgement that they'll open to working with her. To Sumai, she sees both Mei and Chi as good friends of hers, and she's willing to assist them whenever they need that morale boost or emotional relief.

Sumai was a former shut-in, an extremely introverted person that would stay at home or hide from a majority of people out of disinterest or fear. Her parents were worried with how she had been behaving, and often tried to help encourage her to be more social. As years went on, her fear of being alone grew more and more, but she couldn't muster the confidence to do anything. Later in her life, she had to find a job as continuing to shut in would not benefit her moving on, but her luck in finding a job was less than fortunate. Suddenly, she found the opportunity to work for Itami during a coincidental hiring opening. Sumai was still nervous, but as time went on she began to slowly grow more openly and enthusiastically, although it began to reach the point where she'd enjoy pestering other people for the sake of fun (AKA, Present Sumai). However, her upbeat attitude was a way to ensure that she'll continue being around people as well as her workplace without feeling alone anymore.

Sumai was hired before Mei was, so she has more working experience than Mei does. Ironically, Mei has more knowledge about the company more than Sumai. Despite those differences, in terms of both work experience and vastly opposite personalities, the two respect each other very well...in their own unusual colleague-ish work-appropriate ways.

Sumai fights in a bizarre manner; mastering close combat, yet utilizing a wide variety of fighting techniques, such as moves from karate, wrestling, and street fighting. She likes to grab and throw opponents, and other times she enjoys the thrill of body slamming into others. While one would perceive this as extremely dangerous to her health, she's quite fine with it. Sumai has developed an unusually high pain tolerance, so she can withstand a significant amount of power from physical attacks, or heavy injuries.