Koko wa Ore ni Makasete Saki ni Ike to Itte kara 10 Nen ga Tattara Densetsu ni Natteita.

The Hero’s party was attacked by a large group of powerful devils. The party will no doubt be annihilated if this were to go on.
One member of the party, the strongest mage, Rakku, decided to stop the enemies in their tracks.
"Leave it to me here and go!"
"But……"
"Hey, I’ll catch up immediately, alright?"
Rakku mindlessly defeated the enemies, over and over again.
Using his special skill, Learning, Rakku learned the devils’ magic.
As he studied and utilised the devils’ abilities such as Drain Touch, he continued fighting, without rest nor sleep.
The devils got stronger and stronger, but Rakku too rapidly grew.
Rakku battled for 10 years, until no devils came at him.
Rakku...