Teach a new dog old tricks (Neo)

Achievement unlocked! "Teach a new dog old tricks"!

Train a summon in a skill, spell, or style in which you have at least three levels!

+2,600XP

+2,000TP for the summon trained

+1 level in a skill (the one trained, if non-style) for both summoner and summon

Reference
Unlocked in Chapter 113 "A Brief According"