AereA

As simple as the description states.
You must hold 5000 Clefines at once, this is not cumulative,

You get Clefines from killing enemies and breaking jars.

If you don't buy anything from the shops and are pretty thorough in the levels with side quests then you should get this around rock desert stage 1 (obviously not guaranteed but give an indication on roughly where to expect it to pop)

Try not spend money as you need to have 25000 for another cheevo.