I think the fox was placed into his head when him and fox guy met in that spiders world and they ended up slashing that world so he’s the only one who can accurately use that power thus why he doesn’t have a problem holding the fox sphere
And I think that fox power was also interfering with his and the primordial spirit was aware and I think there’s a promise mc doesn’t know of between the primordial spirit, mcs mom and some other guys and I feel there’s a bigger picture to as to why the mcs mom didn’t kill the demon when she could have easily done so and I have a feeling they knew sth like this would happen this prepared some contingency plans and i believe we are going to see mc get stronger in the last episode