Serment: Contract with a Devil – Ending Achievement Guide

This guide is for Sera final encounter. This guide shows you how to fight Sera and how to beat Sera.


I did this around level 42. You can probably manage it earlier. I’d also mastered all weapons for the three characters I used and increased all player stats (but STR) to their maximum in the Mansion. A guide already exists for this.


  • Mage (Player-Character)
  • Maria
  • Dolly

In that order in the party. You can bring more if you want, but we won’t be using them.



  • Weapon: Icarus (Flame Skin, Magic Pierce III)
  • Armor: Mystic Shroud (Elemental Mastery)
  • Accessory: Ren’s Ribbon (Fire Mastery II)

Maria (Mystic Shroud and Jeweled Necklace are negotiable. The extra elemental resistance helps, though.)

  • Weapon: Niflheim (Ice Nova, Overcharge II, Frost Empress)
  • Armor: Mystic Shroud (Elemental Mastery)
  • Accessory: Jeweled Necklace (Fire, Ice, Thunder Resistance)

Dolly (Dragon Tunic and Jeweled Necklace are negotiable. The extra elemental resistance helps, though.)

  • Weapon: Seraphic Bell (Heal II, Purify, Holy Purge)
  • Armor: Dragon Tunic (Auto Regen, Elemental Resistance)
  • Accessory: Jeweled Necklace (Fire Ice, Thunder Resistance)


If you have any of Emilia’s Lunch Boxes, they’re recommended.


Character Roles

  • Mage — She will be your primary, if not exclusive, source of damage. The focus here is twofold: maximize damage potential with Explosion, and absorb fire damage (which you will be dealing to yourself with Explosion).
  • Maria — Your buff vendor. Maria will spend most, if not all, of the battle buffing your Mage.
  • Dolly — Debuff application and removal. Buff removal (from the boss).


If your build is anything like what I outlined in the Preparation stage, your fight should go somewhat similar to mine, with some variance. If any character dies and Sera isn’t already low, just reload.

General Approach

  • Mage — Cast Explosion. Don’t slow down until you have reached Stage III.
  • Maria — Cast Overcharge II on Mage. Don’t stop.
  • Dolly — Cast Purify on Mage or Maria only if they have Freeze or Shock. Cast Heal II on Maria or Dolly if they are low. Cast Holy Purge on the boss if it has buffs. Cast Shadow Cross on the boss (for the chance of Corruption) only if nothing else applies.

Detailed Approach
HP thresholds are far from exact, but are meant to give a general idea of when Sera transitions from one stage to the next.

After a fight or two, you should have a decent idea of how much damage your Explosions are doing, both with and without Overcharge. Keep this in mind, as it will help you to better navigate stage transition times.

Stage I: Fire 20000 HP
Sera begins the fight in her Fire stance. Depending on whether or not you get her out of it in time, you may need to reload. This is because she has two fire attacks. Heat Wave is area of effect, the other is not. The area of effect spell could very well wipe your NPCs. If so, restart.

You want to get Sera out of Fire stance as soon as possible. Your NPCs can usually handle the following stages, but Heat Wave can be devastating.

Stage II: Ice Transition at 15000–17500 HP
It’s possible to skip Stage II or III entirely. A favorable burst will bring you to Stage III immediately, which generally works out better than Stage II. Sera’s Ice Nova (area of effect) will sometimes kill Maria. It’s a toss up. Just burn through this phase.

Stage III: Thunder Transition at 10000–12500 HP
This stage can be a bit tricky. It’s possible to spike your damage too quickly and open yourself up to annihilation in Stage IV. Meter your damage for a turn or two if you have to in order to be certain your Mage and Maria have the MP necessary for a quick burst through Stage IV.

Stage IV: Final Stance Transition at 5000–7500 HP
This is Sera’s ultimate stance. She will begin by casting Overcharge, and what follows is an attack that will likely wipe the party. It is possible for it to miss, but I wouldn’t count on it. It’s also possible to remove the Overcharge buff with Holy Purge, but that isn’t likely to help. Well, it didn’t help me.

The aim here is to get Sera as close to Stage IV as possible without kicking her into the stage prematurely. The idea is as follows:

  • Mage ready with enough MP to cast 1 or 2 Explosions. If you have Emilia’s Lunch Box, now is a great time to use it.
  • Maria ready with Overcharge.
  • You’ll sometimes end up with the Freeze status effect during this time. So keep an eye out. If so, have Dolly handle it. Otherwise, it will blunt your spike damage.
  • Once you feel you’re ready, Explosion away. Just don’t dawdle. Sera can easily knock out an NPC.

Caution: Sera will skip Overcharge and go straight to her instakill attack if you spike her too low (say, below 2500 HP) before she has a chance to cast Overcharge.

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Written by Šailor Cat

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