You’ve likely seen him. The tall, blonde guy with the massive sword and the surprisingly fancy cape standing on a cliff in Taito. In the world of Shin Megami Tensei V: Vengeance, Fionn mac Cumhaill is kind of a big deal, but honestly, he’s also one of the most misunderstood demons in the entire game. Players often treat him as just another mid-game roadblock or a "pretty boy" fusion fodder, but if you know how to actually use him, he's a total powerhouse.
Basically, Fionn is the legendary Irish hero of the Fenian Cycle. In the game, he’s a Genma race demon who hits like a freight train. But getting him into your party isn't as simple as just reaching his level and smashing some buttons in the World of Shadows.
Finding Fionn mac Cumhaill SMT V: The Quest Chain
Most people get frustrated because they reach the Taito region and can’t find his quest. It’s not just you. You can’t just walk up to him. He won’t even talk to you until you’ve basically played social worker for the entire Fairy Village.
To unlock the boss fight against Fionn mac Cumhaill SMT V, you have to complete a specific string of subquests. You’ve got to help Silky with her mandrake problem. You’ve got to deal with the Kelpie and the Girimekhala head. You even need to finish the quests for Idun and Loki. Only after the Fairy Village is "stable" will Fionn show up on that snowy ridge in the North of Taito.
The fight itself? It’s a reality check. If you go in underleveled, he will end your run in about two turns. He loves to spam Mac an Luin, a unique Physical skill that deals severe damage and has a high critical rate. If he crits, he gets more turns. If he gets more turns, you’re dead. Simple math.
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Why Mac an Luin is Actually Broken
So, let's talk about his signature move. In the original SMT V, Mac an Luin was great. In Vengeance, it’s still a top-tier Physical nuke for that stage of the game. It’s a single-target hit, but the damage scaling is wild.
A lot of "pro" players will tell you to just use Yoshitsune for everything because of Hassou Tobi. Sure, Yoshi is a beast. But Fionn has better base bulk and doesn't fall off as hard in the extreme late game if you feed him the right Balms.
- Weakness: Electricity. (Fix this immediately with a Resist/Null/Drain Elec passive).
- Resistances: He blocks Light and resists Ice and Fire.
- The Secret Sauce: His Magic stat isn't actually terrible. While he’s built for Strength, he can flex into a hybrid build if you’re weird like that, though I wouldn't recommend it for Hard mode.
Honestly, the best way to build him is to lean into the "crit-fish" meta. Give him Critical Pleroma and High Physical Pleroma. Suddenly, that Mac an Luin isn't just a hit; it’s a deleted health bar.
The Low-Level Strategy (If You’re Brave)
I’ve seen some crazy challenge runners take him down at level 30 on Hard mode. It’s stressful. The key is using an Oni or something with Taunt and Physical resistance. Since Fionn’s AI heavily prioritizes single-target Physical attacks, you can bait him into hitting a wall.
Just watch out for his Magatsuhi turn. He will stop the sword swinging and drop a Maragion (Fire) on your head. If your team is weak to fire, that’s a "Game Over" screen right there. Use a Fire Dampener. Seriously. Don't be a hero; use the items.
Is He Worth the Fusion?
Short answer: Yes.
Long answer: Still yes, but with caveats.
Fionn joins you around level 66-70 depending on your fusion path. At that point, you’re starting to look toward the endgame bosses like Khonsu Ra or Shiva. Fionn excels here because his resistances are actually very relevant for the Taito boss rush. He stays useful for a long time, especially if you pass down Enduring Soul to him.
He sort of fills that "Heavy Bruiser" role perfectly. He’s not as fast as some of the high-level Fiends, but he stays on the field. He’s reliable. In a game where one bad RNG crit can wipe your party, reliability is king.
Actionable Steps for Your Playthrough
If you want to make the most of Fionn, do these three things right now:
- Clear the Fairy Village: Don't skip those "fetch" quests. They are the literal key to unlocking him.
- Electric Coverage: The moment you fuse him, check your Essence stock. If you don't have Null Elec or at least Resist Elec, go find a demon that does. Fionn with an open weakness is a liability.
- Physical Pleroma Stacking: Don't bother giving him support skills like Media. He’s a killer. Let him kill. Focus every skill slot on Physical damage boosts and Accuracy (Agility) to ensure Mac an Luin never misses.
Fionn mac Cumhaill is more than just a legendary hero with great hair. He’s a cornerstone for any Physical-focused team in the mid-to-late game of SMT V. Go get those mandrake roots, finish the quests, and put the Salmon of Knowledge's protege to work.