I remember that in the arc, the ml locks up the mc with this chain that is said to be impenetrable and with the chain gives the mc a slow acting poison that gradually makes the mcs body temperature to decrease lower and lower until he ultimately dies. The ml regrets his actions after confirming that the mc loves him and the mc "finds out that the ml poisoned him " and that he's dying from people around them in their camp. The ml tries to slow the effects of the poison with his own powers or something like that. If you know the title and arc number, I'd greatly appreciate it!!!