Both dramas are about high school boys who are looked down upon one way or another, and are eventually involved in a water sports team that they establish at their schools.
Both very similar, they talk about boys who train to swim to achieve their dream.
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Tumbling also revolves around "Yankees" or delinquent-like students joining a team sport and struggling/working together. Also you get the same satisfaction of cute boys in tight gymnastic suits instead of tight speedos.
There's the same concept of the school sucking and being rivals with a better school (academic and baseball-wise). Also there's the same actors, Nakajima Yuto and Yamazaki Kento, once again on the same struggling team.