Kiyoshi Mitarai (御手洗 清志, Mitarai Kiyoshi), more commonly known as Seaman (
Slender and of average height, Seaman possesses a slight build, a fair complexion, and delicate facial features. His sandy brown and wavy hair is normally slicked back, leaving just a few bangs dangling onto his forehead, and his garments include a yellow hooded sweatshirt, tight blue jeans, and a pair of white shoes.
When he was bullied by his fellow students in his Junior High School days before he was recruited by Sensui, he wears a uniform identical to Kuwabara's light blue uniform.
He briefly wore a business suit while attempting to enter in the best high school of his home city.
After being indoctrinated by Sensui, Seaman developed a hatred towards all humans, desiring to relentlessly punish all of humanity for its sins and immoralities. At this point, he changes into somewhat of a hypocrite, becoming the same ruthless killer which he despises the rest of humanity for being; although this is largely due to Sensui's influence. However, after witnessing two acts of kindness by Star and kuwabara and thier friends, as well as noticing their views on life, Seaman's outlook on humanity slowly begins to change. He eventually starts viewing humans as good.
He is a self-described social outcast who claims to have been ostracized by his fellow school mates. After his encounter with the near destruction of all humanity as well as helping Yusuke's team to save the world, Mitarai opens up to the world, and gains the confidence to look at the future with an optimistic view on life.
Chapter Black Saga
On their way back from a Megallica concert, Kuwabara and his friends are confronted by Seaman, one of Sensui's
psychics, who takes advantage of Kuwabara's present lack of spirit energy and one by one traps Kuwabara's friends and his step sister star in a manipulated water giant, which acts as a dimensional prison. On the verge of drowning inside Seaman's monster, Kuwabara suddenly manipulates his spirit energy in a peculiar way, creating a kind of spirit sword that can slice through dimensions and barriers. With this new ability, Kuwabara breaks free of the water giant, freeing himself,his friends and his step sister. Kuwabara spares his opponent and even brings him to safety, an action which baffles Seaman to no end, causing him to question the nature of humans.
After awakening at Yusuke's apartment, he is interrogated by the team and tells them about the Chapter Black with such fear and emotion that it lead to Keiko crying. During Sensui's initial confrontation with Yusuke and his friends, Seaman stays in an adjacent apartment with Botan and after an explosion in the apartment building, furniture throughout the building begins to topple, and Botan protects Seaman from a falling bookcase, leaving her fairly wounded in the process. Confused as to why she would commit such a selfless act, Seaman begins to realize that humans are not the ruthless killers whom he once believed them to be.
With a new outlook on humanity, Seaman then briefly assists Yusuke's team in their quest to keep the Makai barrier closed, leading them into Sensui's lair and helping the group defeat the Game Master. Following the final confrontation with Sensui, Seaman returns to middle school, eventually getting accepted into the city's finest high school with his new girlfriend,star.
Power and abilities 
Monster Summoner ( 獣・サモナー , Kemono Samonā ), translated as Monster/Beast Summoner : Seaman himself is unable to fight properly, and thus creates liquid creatures that do his bidding, while he stands back safe from harm. Due to indignation for his troubled past, he has a tendency to brutally torture his victims before drowning them.
Water Manipulation ( 水 ・マニピュレーション , Mizu Manipyurēshon ), translated as Water Manipulation : Once Seaman sheds blood and drop it in water, he's able to form the water into creatures of varying sizes depending on how much blood is used .
- Water Dimension ( 水 ・次元 , Mizu Jigen ), translated as Water Dimension : By combining his blood with water, Seaman demonstrates a limited form of hydrokinesis or water manipulation. The most notable aspect of the water he manipulates is that the inside of the water resides on a separate dimension, making it nearly impossible for one to pierce it.
- Water Monster ( 水 ・獣 , Mizu Kemono ), translated as Water Monster/Beast : By adding his blood to water, Seaman can create indestructible monsters. The more water around, the easier it spreads, and the more blood, the bigger and more powerful the monster becomes. However, the monsters created from a smaller amount of blood seem to be far more agile. Larger amounts of blood create a giant, made entirely of water, that is mainly used to bind and drown victims.
- Since Sensui's Seven each represent one of the seven deadly sins, Seaman represents Envy, based on the fact he targets those who he thinks are weaker than him, and the way he used to look down on himself for lacking skills to succeed and constantly bullied on.
- Like several other psychics who gained power from the demon gate, Mitarai only has S-class spirit power but his psychic power makes him an S-class threat.
- Mitarai is an avid Goblin City player when he is shown being proficient at the tennis mini-game when fighting Tsukihito Amanuma in his territory.
- His appearance slightly resembles that of Koichi Hirose, a main character of the manga series Jojo's Bizarre Adventure: Dimond is unbreakable
- It was identefied that seaman had a crush on star and told her his feelings
|e v||Sensui Seven|
|Members:||Shinobu Sensui | Itsuki | Kaname Hagiri | Minoru Kamiya | Kiyoshi Mitarai | Tsukihito Amanuma | Sadao Makihara | Elder Toguro|