Jyugo is his best friend and the two are extremely close. They usually spend the most time with each other and share a similarly large intellect, with Jyugo being smarter. Uno is not above telling Jyugo about his faults, but cares greatly for him, considering him the only person who truly understands him and their friends. He becomes truly mad for the first time when Hajime beats Jyugo within an inch of his life to calm him after he went berserk.
Uno and Rock initially did not get along when they first met as Uno was annoyed by Rock's stupidity and impulsiveness and Rock was annoyed by Uno's arrogant bossy attitude. Despite this,the two seem to get along in the present time, though they have the least amount of interaction among the four. However, the two do share some things in common such as being the tallest and oldest of the group along with a similar interest in women (though Uno is far more interested and perverted than Rock). In addition, despite being annoyed by Rock's stupidity and love of food, Uno himself shows he does also have an appreciation for good food, at one point sharing Rock's sentiments about wanting to eat a stone oven cooked pizza.
He seems to care for Nico like a little brother, worrying for him when he goes into danger and once ordering an anime figurine online for him, something that made him happy. The two also possess the most artistic skill out of the group, though their skill is catered to their interests.
Like his friends, he enjoys teasing Hajime. Hajime tends to get annoyed with his antics like he does with the others but is usually able to prevent him from wanting to escape by showing him erotic magazines. However, their relationship turns sour after Hajime beats Jyugo, saying that Hajime was a worse monster for what he did and lectured him severely before kicking him out of the cell.