|Relations||Umaru Doma (sister)|
|Anime||Umaru and Onii-chan|
|Japanese voice||Kenji Nojima|
Taihei has shaggy, straight black hair with a sharply pointed strand at the top. He has brown eyes just as his sister does, and a pale skin tone. He is a young man of average build, appearing fairly slim and lacking in any real muscle tone, however, he appears healthy.
Taihei is often seen wearing his work uniform which consists of a black suit with a blue striped tie, black shoes, a thong and a white under-shirt featuring his normal glasses.
Taihei can also been seen wearing a variety of outfits common to young men such as himself such as jeans, button up shirts, t-shirts, etc. He also occasionally wears a blue apron when cooking for Umaru.
Taihei is a kind person and a hard working man, who loves to cook. He is well known for being a pushover and excessively tolerant of other people slacking off such as Umaru or his co-worker, Takeshi Motoba.
Taihei, while polite and well balanced, could be described as a bit of a doormat, as his younger sister constantly walks all over him, making him cook, clean, and buy/do whatever she tells him to. Though Umaru may be unbearable at times, Taihei appears to deeply care for his sister and worry about her future as an independent person as he has admitted that he has spoiled her for too long. Although Taihei does internally express anger towards Umaru during her more "bratty" moments, he often calms down and tries to take a friendlier approach to winning her happiness back.
He seems to have some sort of long-term memory deficiency, as he has trouble remembering certain things in his past. Umaru seems to take the place in his mind of the people he has forgotten.
Taihei is often gullible, being easily duped into doing whatever Umaru tells him to such as her making him miss work so he could help her win a Necolumbus, and lying to him about using that time to relax, until he realized she tricked him into helping her and he is extremely sensitive to massive peer pressure. Back in the past when they were out in public, Umaru would demand that he buys her something and if he refuses, she would pretend to cry in her outside form or throw a massive tantrum in her inside form to turn people against him for hurting her feelings.
He has also shown to be especially oblivious to other's love interests, as shown with both Kanau and Ebina who have feelings for him.
It is known that he has been living in his residential area for a long time as he remembered walking home from school with his mother when he was small. Considering his father is extremely wealthy, his mother was presumably a mistress.
Taihei has been in his apartment for a minimum of a year as he noted that Umaru had moved in with him about a year ago.
- In high school, he was known as Demon Taihei because of how pointy his hair is and because he got perfect scores all the times, just like his sister.
- Taihei loves cats, as seen in episode 7, and he even dreamt of petting them.
- Taihei is afraid of driving vehicles.
- Umaru greatly resembles the siblings' mother, which might explain why he's extremely tolerant of Umaru and her strange habits/behavior most of the time.
- Taihei works for Diamond Service.
- He has a dislike for chocolates and anime.