Brilliant Eidolon Shard: What do I do with it specifically?

[Genji]

I heard it unlocks the Way-Bound passives but "how" exactly?

Where does the option to use it come up?

Or is it a glorified resource?

[Kalvorax]

it will probably come up after you get max rank in a way-bound passive.

[Phatose]

Focus tree, same place you level up focus nodes, once a way-bound node is maxxed.  At least, gives you the option there when a node is maxxed and yells if you don't have a shard.

[NekroArts]

You'll be able to use them to unbound way-bound passives when its "max rank" and a notification appears above it showing how much focus is needed plus a brilliant eidolon shard. By using the necessary materials, that skill node is then usable in all other focus tress. For instance, I recently unbound the node that increase my Operator's HP  from Vazarin. Now when I use the other schools I will always have increase HP.

Edited October 16, 2017 by NekroArts

[Aurea_Hiigara]

You also require 1 million (yes, million) spare focus points in the tree of the skill you're unbinding. Basically, you turn a Vazarin passive into a Permanent passive as an example.