Look at FSC.

It's called Shadow Fire.

I think that there needs to be a weapon which utilizes this fire. I want it captured and harnessed!

(Note: This is a shoutout to all those forum goers who say that there needs-not be a shadow weapon which deals fire. However, I see no reason for this not existing. Actually, I would go as far as to suggest that a miniature version of Vana's mace would drop from Vanaduke as a rare drop. It would work like a Troika but would deal the Fire status and Shadow damage.)