|Other names||Big Brother (by Goromaru)|
|Family||Unnamed Grandfather †|
Kasumi (younger sister)
|Physical and Vital Statistics|
Tatsumi has messy black hair and tired golden eyes. He is tall and is shown to have a quite muscular body, managing to taking down a grown man with only a few movements.
Tatsumi is a nice, selfless guy and isn't particularly concerned about his new free-loader. Although he isn't happy about the larger water and gas bills, he is a frugal and knows it's not cheap keeping a merman supplied with fresh, warm water. He is very concerned about finances and seems sullen and disinterested, but he actually cares about his new friends.
Usually he will entertain his guests and teach them about the human things they don't understand, but sometimes he's the one who has to reel them back in and snip their (usually Wakasa's) dreams before things get too out of hand.
As a child, Tatsumi spent a lot of time in his grandfather's house and after he died, he stayed to live in the house because it was close to his school.
When he was around ten, Tatsumi fell into a river while he was fishing. He was then rescued by Wakasa, who after being offended by Tatsumi, he threatened him so he will not tell anyone about his existence. This made Tatsumi to hate the water, taking baths and mainly, the slime.
Years later, Tatsumi found Wakasa stranded near a river by the upstream dam and thinking he was hurt, he took Wakasa with him to his house. At the time, Tatsumi didn't seem to remember him and was shocked to find out he was a merman, but decided to let him stay in his bathtub anyway.
- His hair freaks out in humidity.
- He has a bad back from often sleeping in the bathroom.
- He is often reminded of sea food dishes when around Wakasa and friends.
- His favorite food is steamed crab, second being octopus.
- He has great upper body strength.
- Wakasa's scales often stick to his clothing.
- He works at his cousin's liquor store.
- He is popular among older women.
- He occasionally breaks the third wall.
- He hates slime.
- His name come from the "Kuzuryu" river.