From Sonic Retro
Chao Adventure refers to the VMU minigame that acts as a trainer for Chao in Sonic Adventure. In the game, the Chao goes on an "Adventure Walk" where skills are improved, depending upon the selected course. Along the way, the Chao may find fruit in treasure chests, encounter bullies and meet characters from Sonic Adventure who bear fruit, with the exception of E-102 Gamma.
By connecting two VMU units together, two Chao can be bred.