It's about time to add Coil story mode, isn't it ?

[Moqi]

snip

I honestly can't recall any big storyline related to secret/optional bosses in other FFs. The FFXIII trilogy certanly had none, XII harderst bosses were hunts, FFX's Zoolab didn't have a storyline either... maybe FFX-2 with Trema, although I have personally never fought him so I don't know how much storyline is there. And the Cups have some silly storylines for the monsters but they're hardly as important as what happened to Eorzea's biggest threat. Did FFVII's weapons have any stroyline to them?