Taihei Doma (土間 大平, Doma Taihei) is the older brother of Umaru Doma and the deuteragonist of the Himouto! Umaru-chan series. He is also the main protagonist of the Himōto! Umaru-chan: Himōto! Ikusei Keikaku visual novel game.
Taihei is a man of less than average build, appearing fairly slim and lacking in any real muscle tone, however, he appears healthy.
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 light, pale skin tone.
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
Because of his perfect little sister turning into a hardcore otaku while living with him for only a year, his capability as a responsible figure is questionable.
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.
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, but considering his father who is extremely wealthy probably his mother was 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.
- 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're out in the public, Umaru demands that he buys her something and if he refuses, she'll 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).
- 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.
- He tries to prevent Umaru from buying unnecessary stuff online and somehow she knows the information on his online shopping accounts.
- It is revealed that the siblings used to live in a large apartment and that their father is president of Doma Corp, but Taihei moved out for some reason.
- Although Umaru makes his life miserable most of the time, Taihei later realizes that his life would be boring without her.
- Taihei likes cats as seen in episode 7 and he even dreamt of petting them.
- Taihei is not very fond of chocolates.
- Taihei likes Ebina's kitchen due to it being clean and it unusually has two fridges.
- Taihei later finds cooking interesting.
- Taihei always tries to conserve money.
- Taihei is afraid of driving vehicles.
- He is extremely clueless to both Kanau and Ebina having feelings for him.
- 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 rarely scolds his sister, unless Umaru goes too far with her behavior.
- In chapter 30, when Umaru starts riding a bouncing animal, Taihei realizes that Umaru is still a child.
- He doesn't like anime.
- Taihei works for Diamond Service.