When farming Falna there is a small chance of getting a Heroic Falna (The rainbow orb thing that is used for getting characters to 6* and Limit Breaking).

There is a key on the bottom left corner of the Falna Quests page. This key can be used to increase your Heroic Falna drop-rate for 30 minutes.

The reason you want to use it sooner is two-folded.

• You can only hold one at any time. That's it.

• You get one given every Tuesday, according to the game's Help guide.

Sundays are probably the best day, in general, to use them since all Falna chambers are open all day. It's a great thing to use while farming Falna. Having Heroic Falna around will make it much easier when you are trying to 6* or Limit Break characters since the drop-rates do appear to be too low to be acquirable on demand.