I had not even realized that Ryu Ga Gotoku Studio made Monkey Ball 'cause they used to be Amusement Vision, in fact their first four games were
SpikeOut (playable in Like a Dragon)
Planet Harriers (c’mon!)
Daytona USA 2001 (the Dreamcast one)
Super Monkey Ball
And their old head Nagoshi had also produced Daytona 2.