Madotsuki's Story/guide

Guitar
Enter the green door. Go left and interact with Pirori.

Black Rose
Enter the wooden door. Go right and interact with Monoe.

Biscuit
(Black Rose effect is needed).

Enter the blue and white door. Use the Black Rose effect to jump/hover over the blocks and go north-east. Get up onto a platform with a large cup on it then hover up and to the left until you disappear off-screen and you seem to be moving along a row of blocks.

Move to the left until you appear on screen again. Go left and interact with the biscuit.