Press space to start the game. You’ll get a menu with 2 options in Japanese.
It aks you to continue a saved game or start a new game.
Choose new game by moving the cursor to the 2nd option (move cursor key down and press space key)
Then press space key again to confirm starting the game. The game will start.
Cursor keys: Move | Space = Jump | Shift = Fire
Important: If keyboard does not respond, click with the mouse on the game screen to enable keyboard controls.