Memory Doors

Memory Doors (記憶の扉) are the equivalent of optional side quests from other games.

Background
Memory doors are scattered around Phantasma, with each door providing side story episodes in the form of cutscenes, interactive flashbacks, scripted battles, and minigames, and providing a reward on completion.

There are 25 doors in total, split into three types:
 * The Moon Doors (月の扉) number 5 and provide much lengthier stories which often have interactive elements, such as being able to move around a city or have dungeons with normal encounters.
 * The Star Doors (星の扉) number 15 and provide (usually) short stories.
 * The Sun Doors (太陽の扉) number 5 and exclusively provide minigames.

Mechanics
Each door has an associated riddle. If the party satisfies the requirement set forward, the door can be opened. Some doors instead (or in addition) require an entry battle that must be won to see the contents.

The Recluse Cube can be interacted with to warp between any previously encountered door.