Here is the full list of all 20 My Best Friend Kouta achievements.
Win the Chess Championship.
Get the game Slutty Bikini Ninja Gang.
Get the game B.F.A. Vengeance.
Beat the game Slutty Bikini Ninja Gang.
Beat the game B.F.A. Vengeance.
Complete the tutorial.
Reach the maximum Mental Energy.
Reach the maximum Physical Energy.
Get the Super Battery.
Finish cleaning the square.
Find the first volume of Autumn.
Beat all opponents in Chess.
Go through the first date with Evie.
Work for the first time in the Museum.
Go through the second date with Evie.
Find the second volume of Autumn.
Get the game Hole Raided.
Beat the game Hole Raided.
Finish cleaning the park.
Go through the third date with Evie.