What is meant by "consumed" is getting absorbed by another being turning them into part of that being's soul strength.
Of course, most beings couldn't do this. But Muku being himself could probably do it.
Nightmare had scanned his soul. And he definitely had the capability. Which was why it hadn't acted rashly...
{Don't bother. I think I understand what is going on... In fact, come here for a second and let's talk it out...} Muku spoke again.
Then without waiting for Nightmare to say anything he dragged it into his mindscape.
And just like that, in a vast clearing with green grass and a grey sky, Muku and Nightmare appeared.
Muku's soul looked exactly like how he looked physically.
However, Nightmare looked quite different.
Instead of the threatening giant that terrorized the girls, it looked... even worse...
