Crystal boarder
Win race mode on the expert difficulty level and finish better than all the EAD scores on the time attack and trick attack modes. Then, select Akari Hayami, hold C-Left, and press A at his statistics screen.

Gold boarder
Enable the "Transparent character" and complete "Match Race" on the expert difficulty level with that character. Then, select Kensuke Kimachi, hold C-Up, and press A at his statistics screen.