Ucchies
Ucchies (ウッチーズ) is the combination of Mr.T and his brother Hiro, who provides the vocals to most of these songs. They have performed several songs together in IIDX and Pop'n Music. They're also a band outside of Bemani known as Dream Line Out.
Not to be confused with Ucchies Z (ウッチーズZ), which involves Mr.T by himself with an unknown female vocalist.