Fire Wand is unlocked for all characters after destroying 20 Torches and is the starting weapon. There’s a character (Arca) who starts with this weapon but you only unlock them after getting this achievement lol
Upgrades in this game are random so this may take you a few level ups before you can get the weapon to level 4 so I would suggest pairing the fire wand with something with a faster fire rate (Cross, Magic Wand, etc) if you are struggling to survive long enough to get the 4 levels.
Keep in mind that you can have a maximum of 6 offensive and 6 support items, so if you're struggling to get any of the weapons to appear it might make sense to try to force the game into giving you less variety by taking on items instead of upgrades or, alternatively, biding time by getting upgrades to get more chances to get what you need.