Before dying in the accident where he gets hit by a truck, he worked as poor fortune teller and a part time computer mechanic. He is currently affiliated with the Tanmoku household.
Before dying, Keika appeared as a normal twenty three year old. After his death, his physical appearance turned back towards his middle school look as that was the time where he was the most innocent and happy.
Keika has dark blue color hair with olive green eyes. Although in the second season his eyes appear to be a more blue color than green after he was taken over by the first Youmeishi. His long hair is tied into a low ponytail with bangs covering his forehead and the side of his head.
In his usual spirit form he wears a traditional Chinese jade colored shirt with white pants. In his advanced spirit form his hair is longer and his attire consists of almost complete black. Black long robe over black shirt, black pants, and black obi tied at his waist.
Keika bears a striking resemblance to Shisei.
Keika also wears a blue hair ribbom that is braided with Ki's first baby hair. But he cuts it off in the end to save Ki.
Keika has another form where he takes on the appearance of his ancestor You Nei and he wears a full black outfit and his hair becomes longer and slightly darker.
Keika You is a boisterous young man with a pure heart. He is quick to make friends and cares about the people that mattered to him even after he became a spirit.
He is usually positive most of the time and tends to act idiotic like getting overly excited over simple things like flying when he found out he could when he became a spirit instead of getting worried that he is actually dead. Because of this character a lot of people he comes in contact with views him as a 'monkey' or a 'clown'.
Despite all that Keika is innocent and gentle. Even when the Tanmoku household looked down on him for being a 'lowly spirit' he never raised voice against them neither did he refute them.
In his 'Shisei' form he is more confident in his abilities and might come out to be a little bit arrogant.
Ki Tanmoku- Ki Tanmoku is his Master, and Keika serves him as his spirit shadow. Keika considers Ki as one of the most important person in his life and someone he would serve the rest of his life for. In the beginning Keika viewed Ki to be an arrogant, rich boy who was pretty cold even to his own fiancee. He would often bicker and argue with him and threaten him that Ki shouldn't let his guard down because Keika will take his life if he wants to.
Keika was reluctant to be Ki's spirit shadow in the beginning until he learned that he would be turned into an evil spirit if he didn't. Once he became Ki's spirit shadow his relationship with him was still rocky but later in the episodes he has grown more attached to Ki after knowing the latter's gentle side.
In an episode, after accidentally stabbing Ki, and was imprisoned by Jimei, he cried and begged Shin Shiyou to let him visit the Yomeishi and make sure that he was alright.
When Shin Shiyou broke his imprisonment he rushed to Ki's side and promised his loyalty to the man while he was asleep- vowing to stay by his side and follow him to the ends even if it was too late. He has grown to be protective of Ki and wouldn't let a single person harm him.
It's also hinted that Keika might have developed romantic feelings for Ki. In episode 6, when Ki kissed Keika to breathe "life" into him, Keika pushed him away and comically spat his kiss. But in episode 10 when Ki kissed him again, Keika blushed and asked him what it was for instead of pushing him away.
Keika also sacrificed his life to save Ki. Cutting the hair braid and tearing his own soul apart so Ki would regain his spiritual powers and defeat Shito Ritsu. But Ki never did get his powers in that action. When Keika finally 'dies' and was going to cross over he remembered that he made a promise with someone and couldn't leave that person alone. He came back when he heard Ki's voice calling out to him.
Tanmoku Mistress- The mistress of the Tanmoku family and Keika has a healthy relationship equivalent to a mother-in-law and a "daughter-in-law".