User blog comment:IamJakuhoRaikoben/Chapter 495: I'm Hungry As Hell, Review./@comment-5672982-20160725171838

Could it be that God Serena's epithet is a reference to the Yamata no Orochi, hence the eight Dragon spirits he summoned?

That said, Storm Dragon Slayer seems to be interesting, for although it doesn't clearly show its element, it appears to be a upgraded form of Lightning Dragon Slayer magic, as Storms are often associated with lightning and thunder.

So that makes five DS magics in total:

Cavern Dragon Slayer Magic --> Earth Purgatory Dragon Slayer Magic --> Fire (Hellfire) Gale Dragon Slayer Magic --> Wind Sea King Dragon Slayer Magic --> Water Storm Dragon Slayer Magic --> Lightning

That still leaves three left. Looks like the idea of the DS magics being related to the Eclipse Gate Dragons appears to become true. So the last three should be Light, Darkness and Diamond/Adamantine based.

That said, too bad God Serena is going down faster than you can crack a egg. Gildarts is going to thrash him alive.