At the center of the chaotic world of Ichio Junior High is the infamous Kimengumi, a group of five male students known for their bizarre quirks, eccentric personalities, and a shared history of repeating grades. The leader, Rei Ichido, is a simple-minded boy who can perform odd tricks with his body. His companions include the aggressive and hearty Go Reietsu, the lecherous but surprisingly brainy Kiyoshi Shusse, the easygoing and food-obsessed Jin Daima, and the feminine and gentle Dai Monohoshi. Their shared philosophy is to confidently express their unique personalities, no matter how much they are ridiculed, aiming to become the "seasoning that adds taste to the world".

The group’s otherwise bizarre antics catch the attention of Yui Kawa, a pretty transfer student, and her strong-willed best friend, Chie Uru. Intrigued rather than repelled, Yui begins tagging along with the Kimengumi, while Chie often acts as the comedic foil to their absurdity. Their school is also populated by other distinctive cliques, including the handsome and popular Irootokogumi led by Sho Kireide, the athletic Udegumi, a delinquent gang called Bangumi, and the tough all-girl crew Omegumi.

The series follows an episodic format, chronicling the bizarre adventures of the group as they navigate school events, club activities, and everyday life. The comedy often involves the members using odd abilities, such as transforming their bodies or limbs, to perform incomprehensible feats. The narrative initially focuses on their time in junior high before they move on to the fictional Ichio High School, where the story continues to focus on high school life with a heavy comedic touch. Throughout the series, the Kimengumi engage in rivalries with other groups, deal with their unique families, and participate in school events, all while Yui gradually develops feelings for the oblivious leader, Rei.