Seems interesting.... though having 6 weapons would probably be a bit much to have sheathed xp. If I were make a simple concept I'd take a note from kh2 Master form and bbs wingblade.

Instead of 6 blades you have 3 blades, one held by the person, one they use psychokinisis to control it (like sora) , the last one stays holstered but would be easily used psychonetocally like the other blade. They have 2 gauges, one that is just for building up till form shift (BM gauge for the example) the other used similar to drk blood gauge (let's call it the BD gauge for the example). Their mp drains like hw drk, has a skill that can use the BD gauge to restore some mp like sb Delirium.

Build up the BM gauge to activate blade master form

Get 3 more aetherial blades for 6 in total. Cool shit ensues