Ideas To Defeat Dante

How so?
Sephiroth can use something like untouchable?

Ultimately, Dante can defeat anything with Royal Guard. Block&Charge could block anything, Release will unlease the charged energy (back to the attacker, or anyone), and Ultimate can absorb attacks (which heals Dante, it's used for its blocking more than anything, though).

If you are saying that Dante cannot REACH Sephiroth because of the range advantage... well, Dante has his firearms and quite a number of range attacks, and he could use the Trickster style instead of Royal Guard and teleport to the enemy.

EDIT:
But to be honest, Royal Guard can pretty much be the answer to anything. It blocks any move, including magic, non-elemental, area of effect attack such as explosion, whole area lightning, and stationary traps.