Darin is the owner of the shop drain's mart. He is a boss that appears in episode 4 in east street 11 along with his cat.

He doesn't seem to be resistant to anything but his weakness seems to be poison and fire weapons

Ranged weapons are good so you can save health. Just eliminate his cat who is all so in side first.

when you beat him and his cat there will be a safe that has bear knuckles inside witch is a poison weapon.