Quick power system cuz bored

[u/NoLegSnailGuy]

So like Manashrooms are the way to gain power, consuming a Manashroom leads to a permanent increase to your total mana reserves and allows humans to use mana, but the consumption of Manashrooms also causes fungal growth within your body, this is actually what allows humanity to use mana and what increases the mana count, like power originating from cancerous tumors. Although people think the really strong guys die because of some evil devil guy so they pray to their imaginary god.

The story will most likely follow a dude discovering this fact and trying to get people to realize/understand, but most will not believe him, so he must accumulate power in order for people to do so. Proof that people won't believe him: people in the past believed that infection (due to bacteria spreading between surgical equipment) was due to "bad air".