Obtained from Journey to the West Event.
Grants +1 ATK on Skill Activation. A pretty cheap alternative to some other cards with the same effect.
But if Ginkaku happens to be subbed on the same card, you also get a 7% Skill Boost (alongside Ginkaku's 7% Skill Boost and +1 DEF).
As such, the two together make for pretty good subs.
Kinkaku means "Gold Horn". In Journey to the West, Kinkaku and Ginkaku are brothers who were in possession of several treasures including the Bansho Fan and the Crimson Gourd.