Originally Posted by Ancarius

Skillblooms only increase the skill level by 1 with a 100% chance. Equipment Slots always need to be done with dupes.

Not quite. Certain events have featured dressblooms that opened equipment slots, though they only worked for the featured girl. (I think the event-specific skillblooms worked for any girl at one point, but they fixed that before the dressblooms became available.)