Sen is a young man with dark, shaggy hair, and dark eyes, which are rather thin and lazy-looking. He seems to have a modest athletic build, the same as most of his classmates, and a slight tan.
His hero costume appears to be a windbreaker with rings around the base of the neck and arms. Over this, he wears a large trench coat and gloves.
Sen is a stoic person who remains mostly calm and focused during many occasions. He is also shown to be more mature than Neito Monoma, telling the latter to quit provoking Katsuki Bakugo and focus on his goal during the Cavalry Battle.
Despite his serious demeanor, Sen can sometimes warm up during times when he drops his solemn behavior, such as when he shows enthusiasm in fighting against Mashirao Ojiro during the Joint Training Arc.
Volume 22 mentions that he's rather belligerent in terms of personality and often gets dragged along in his friends' antics. Sen is also described as an "ikeman", having the appearance of a good-looking man. 
Overall Abilities: While the extent of Sen's abilities have yet to be shown, he does possess some proficiency in close quarters combat. By using the gyrating effects of his Quirk in tandem with his hand-to-hand combat abilities, Sen can deliver powerful spinning attacks that can damage his enemies, especially if he uses his drill gloves. During the Joint Training Arc, Sen used this fighting style to fight on par with, and nearly overwhelm Mashirao Ojiro, an experienced martial artist. Before he overpowered Mashirao, Sen was overtaken by Tenya Iida, and whilst being carried away, Sen stated he wasn’t using his full power.
Gyrate (旋回 Senkai?): Sen's Quirk allows him to rotate any part of his body like a drill. The effects of Gyrate turn Sen's limbs into something akin to large rotary tools. This enhances his hand-to-hand combat abilities significantly.
Drill Gloves: Sen wears gloves with a spiral pattern on the fingers. These spirals act like a drill and cut into an enemy, thanks to his Gyrate Quirk.