|Members|| Shun Kakei|
|Jersey Color||Blue and gold. Jerseys are blue, on both sides and on the shoulder protectors are gold scales|
|Mascot||Poseidon, the ancient god of Sea, with Trident an wave in the background|
|Helmet Logo||two golden fins|
|Team Chant||Poseidon Go Splash Go|
Kyoshin Poseidon is a football team from Kyoshin High School that the Deimon Devil Bats face in the Autumn Tokyo Tournament. As their team name suggests, the Poseidon's theme is based on water. Their strategy depends on the great height of their ace players, including Shun Kakei and Kengo Mizumachi.
The Kyoshin Poseidon's uniform consists of: standard football padding with an overshirt, pants, knee high sports socks, and cleats. Their colors are: green highlights with scale designs on the sides (manga) or on the shoulders (anime) and a blue base color, mimicking the colors of aquatic fish.
A team that was underestimated until new rookie stars showed up and made Kyoshin’s the tallest football team in all of Japan. In addition to being tall, the players of Poseidon have great technique, making their defense sturdy and stonewall-like. They are one of the Deimon's most dangerous rivals because they contain the two aces Shun Kakei and Kengo Mizumachi which are both known as a "Golden Pair".
(筧駿, Kakei Shun) The Poseidon's fourth-tallest player (202 cm) and de facto captain, Kakei is the first character to allude to the existence of a "real" Eyeshield 21 in the series. Shun attended middle school in the United States, where he witnessed the play of this true Eyeshield 21, a running back for Notre Dame University's affiliated middle school (later revealed to be Yamato Takeru). Amazed by the prowess of a Japanese player, Kakei became reinvigorated with American football after having been frustrated by his inferiority to the American players around him. When Kakei's team Arizonia University's affiliated middle school played against Notre Dame, Kakei and Eyeshield 21 played against each other on a single play, and while Kakei lost, Eyeshield 21 promised to play him again. Kakei trained hard, becoming the team's ace player.
Mizumachi is the Poseidon's other ace player along with Kakei. He is a lineman who, though not very bulky, is formidable because of his speed and great height, which he uses to his advantage. Mizumachi is considered a natural athletic prodigy, and he was highly sought out by his middle school's athletic clubs, and he chose the swimming club. He joined the American football club because of Kakei's aspiration to win the national championship, which matches his own drive, and he quickly became a talented lineman. Unlike Kakei, Mizumachi is rarely serious, instead being energetic, cheerful, and sometimes rude.
Although the captain of the team and a third-year student, Kobanzame is an incredibly meek person with little capacity for leadership. Additionally, he is not very talented, though he trains hard along with the rest of the team and his play as a quarterback is generally mistake-free.
Ohira and Onishi are a pair of first-year linebackers for the Poseidon and are the two tallest high school American football players in Japan, at 205 and 204 cm respectively. They have shared an intense rivalry since childhood, and each claims to be Kakei's first disciple. They address Kakei as "sensei" despite his being in the same year as them, and their actions are generally foolish. However, despite not being as good as Kakei, they are skilled in the use of the techniques he has taught them, and together all three form the Poseidon's "High Wave" defense strategy.
Kyoshin's offensive and defensive strategies largely depend on the strength of their tall freshman players. On offense, Mizumachi serves as a blocker for Kobanzame and the team's less-talented running backs. Additionally, on passing plays Mizumachi buys time for Kobanzame to complete passes. The team's true strength is on defense, where all four of their tall players play. Aside from Mizumachi's ability to break through blockers, the linebackers Kakei, Ohira, and Onishi form a powerful barrier behind the line, termed the High Wave. Using hand techniques, which Kakei has taught to the other linebackers, the team is able to break through lead blockers and Kakei is able to stop most running backs; on the other hand, their great height enables them to stop forward passes. The High Wave can be made stronger if Mizumachi lines up as a fourth linebacker, creating a 3-4 defense formation called Poseidon. Although Mizumachi's absence from the line theoretically makes running through the middle easier for opposing offenses, the four are generally able to stop most running backs with little physical strength from advancing due to their physique.