Kei Tsukishima (月島蛍, Tsukishima Kei) is a first-year middle blocker at Karasuno High. He is currently a college student and a middle blocker for a Division 2 team in the V League. After graduating, he will work at the Sendai City Museum. He has an older brother, Akiteru Tsukishima, also a volleyball player.

Tsukishima is very tall and has an average build for a volleyball player. Despite being only a first-year, Kei is the tallest player at Karasuno. He has short, slightly tousled blond hair, golden eyes, and pale skin. Tsukishima can often be seen frowning or with a mischievous smirk on his face.After joining the Karasuno volleyball team, Kei wears the Karasuno uniform with the number 11, black knee pads, and white sneakers with green stripes during games. He is also the only player on the Karasuno team to wear glasses. After chapter 109 of the manga, Tsukishima began wearing special sports glasses given to him by his brother. Outside of games and practices, Tsukishima wears a black gakuran, the Karasuno men's uniform, and headphones around his neck. The brand of these headphones appears to be "Somi," which is a play on the Sony brand. He has been seen wearing various shirts with crescent moons on them, which plays on his name "Tsukishima", with "tsuki" meaning "moon".

Facts:Favorite food: Strawberry pie.Current problem: Since the start of high school, he's once again been asked about how to pronounce his name.

The character for his name (蛍) means firefly and can be read as Hotaru or Kei.

Tsukishima wears white sneakers with green stripes.

His zodiac sign is Libra.

He has the third-smallest appetite in the series, often causing his teammates and upperclassmen to worry about his health.

His BMI (Body Mass Index) is the lowest of the male characters in the series.

He has a habit of fiddling with his fingers when nervous, which is especially noticeable when he asks Coach Ukai for blocking advice.

He's usually seen with his white Sony headphones (Somy in the anime, to avoid copyright issues) around his neck when not practicing or playing. Tsukishima appears to be a good student, as he is in class 1-4, known as the college preparatory class.

His birthday falls on the Harvest Moon Festival, which is celebrated during the Mid-Autumn Festival.

He keeps a stuffed dinosaur on a shelf above his desk. Whether he actually likes dinosaurs is unknown (though it can be assumed he does). This is revealed in the chapter "Let's! Haikyuu!!."

Tsukishima is often compared to the moon, and Hinata to the sun, due to their surnames and contrasting personalities.

In a poll conducted on Charapedia (a Japanese anime and manga database) about which anime character parents choose as the basis for their future child's name, Kei ranked ninth, with 98 votes among female respondents. In Haikyuu!!: One Shot (the manga's pilot chapter), Tsukishima was a second-year student, while Hinata and Kageyama were first-years. He was also 186 cm tall.

Furudate chose Tsukishima's name because "his family name has 'moon' (月), as opposed to Hinata's 'sun' (日). But I called him 'firefly' (蛍) because he can emit light himself."

In the first Haikyuu!! popularity poll, Tsukishima placed 8th with 3,407 votes. In the second, he rose to 4th place with 8,305 votes.