This song is not Japanese.

According to the query of Kuwo Music, "Rainbow Beat" is not Japanese. It is a song written and composed by Chinese lyricist and composer Li Maoyang (T2o). The song was sung by Soap Fungus, Yi Yan, Yinque Shiting, Zhao Fangjing, and Xigua Kune. Released on February 4, 2020. Part of the lyrics are excerpted: Don't wait any longer, keep watching and wandering, and watch the stars and the sea on the journey.