Songwright

They are an NPC in the Song room(Guild Base). They can be hired after building 9+ rooms for 20,000 Notes.
They can upgrade your mantras of any attunement including attunementless. Unlike the other mantra trainers, they cost 50% more Notes per upgrade, totaling 1500 notes per level 5 mantra.
Costs for each level up:
* LVL 2: 150 notes
* LVL 3: 300 notes
* LVL 4: 450 notes
* LVL 5: 600 notes