Board Thread:General Discussion/@comment-26849575-20160315015552/@comment-27701762-20160315020653

Ah.

Well there's no indication that X amount of power is needed to erase the world. Flowey's 6 human souls allow him to do a lot of weird stuff, but it's not clear what he actually does.

But anyway, Chara doesn't have the equivalent of 2 human souls. Insofar as Chara is in control of Frisk's soul by the end, Chara has only one soul. But by earning EXP, Frisk's/Chara's power increases, and the basic idea is that once LV hits 20, Chara has a power that trumps the power of the human souls. So on the Genocide route, the one human soul is becoming increasingly more powerful, until it reaches a point where Chara can erase the whole world.

So I guess one way you could put it is that LV 20 is equivalent to 6 human souls (insofar as you want to say that 6 humans souls are needed to erase the world).