You can get the Ultima Weapon by beating the last boss of the Mirage Arena’s Arena Mode—Iron Imprisoner IV.
This is one of the most challenging battles in the game, but since the Ultima Weapon is among the best keyblades in Kingdom Hearts Birth By Sleep, the grind is most definitely worth it!
TABLE OF CONTENTS:
Obtaining Ultima Weapon (Step-By-Step)
To get the Ultima Weapon, the first thing you need to do is go to the Mirage Arena, which is located at the upper-left corner of the map:
World Map (Mirage Arena)
Next, choose whether you’d like to play in Offline or Online mode at the Mirage Arena.
It would help to have a high-level player carry you throughout the battles ahead, but clearing them all on your own in Offline mode is doable if you’re prepared.
Mirage Arena (Play Mode)
Next, go to the Arena Mode to reveal all thirteen events available—all of which are PVE boss battles that go up in difficulty the more you clear.
If you’d like to see all the bosses you can fight in the Mirage Arena, feel free to visit the following article:
Kingdom Hearts Birth By Sleep: Complete Mirage Arena Bosses Guide (Coming Soon!)
Arena Mode
After revealing all of the bosses you can battle in the Arena Mode, you’ll have to make your way through to the last stage, which is called the Villains’ Vendetta.
This is the stage you’ll have to beat if you want to unlock Ultima Weapon:
Arena Mode (Villains’ Vendetta)
Villains’ Vendetta has a total of eight rounds, with each round having you battle strengthened versions of the bosses you’ve fought from previous stages.
In the eighth round, you’ll encounter the Iron Imprisoner IV, which is the strongest of all eight bosses on the stage.
| Stat Types | Imprisoner IV Stats |
| HP | 1,500 HP |
| Defense | 19 DEF |
| Strength | 16 STR |
| EXP | 0 EXP |
| Physical Weakness | x1.00 (Neutral) |
| Fire Weakness | x1.00 (Neutral) |
| Blizzard Weakness | x1.00 (Neutral) |
| Thunder Weakness | x1.00 (Neutral) |
| Dark Weakness | x1.00 (Neutral) |
To prepare for this battle, we recommend equipping abilities that increase your survivability such as:
- Second Chance
- Damage Syphon
- Leaf Bracer
- Fire Screen
- Once More
- HP Boost
- Cure Boost
If you’re planning to beat Iron Imprisoner IV solo, we highly recommend spamming your dodge to not get caught by even one of its attacks, as this boss can stun-lock you until its combos are over.
Villains’ Vendetta (Iron Prisoner IV)
It’s a common consensus among all Kingdom Hearts Birth By Sleep Players that Iron Imprisoner IV is among the worst bosses in the game, mostly because its move set is downright broken and difficult to avoid:
| Imprisoner IV Moveset | Description |
| Volcano | The Iron Imprisoner IV burrows into the ground before bursting out from under the player, dealing heavy damage and staggering them. |
| Berserker Charge | The Iron Imprisoner IV covers itself in flames as it charges forward—all while swinging its massive hammer as it moves. |
| Red Wall Flying Bullet | The Iron Imprisoner IV teleports out of the arena before enveloping the stage in crimson red and sending burning debris that the player must dodge flying all over the place. |
| Explosive Fire | The Iron Imprisoner IV sends out a wave that sucks players towards it, right before exploding and teleporting to another location and doing it all over again. It executes this move up to three times, one after the other. |
| Spirit Rage 2 | The Iron Prisoner IV spins around and dashes all over the arena, making players who are caught unable to retaliate until the rotation is done. |
| Flame Prison | The Iron Prisoner IV traps the player within its former prison, restricting their movement and skill use. To get out, the player must destroy the prison using their normal attacks. |
The best strategy for this boss would be to attack it from a distance with Shotlocks, then spam dodges to get away from it whenever it activates a skill.
Also, bring at least two copies of strong healing Command Skills (preferably Curaga) to guarantee you can sustain yourself the whole fight in case you miss a dodge.
Iron Imprisoner IV (Boss Intro Cutscene)
Using melee attacks against this boss will put you at a disadvantage, but if you’re daring enough to get close, using Thunder Surge as your offensive melee option would be ideal as it gives your character invincibility when cast.
Just remember to only cast Thunder Surge if you’re confident that you won’t be countered by the boss after you use it!
Final Round Victory!
Once this boss has been beaten, you’ll then receive the Ultima Weapon—one of the best Keyblades in Kingdom Hearts Birth By Sleep!
Using Ultima Weapon In Combat
Ultima Weapon (Keyblade Description)
When equipped, the Ultima Weapon gives your character Strength 7 and Magic 6. These stats are excellent, even if we compare them to most other high-tier keyblades in the game.
It also gives you a strong balance between Strength and Magic, which means that Ventus, Terra, and Aqua will all benefit from using it.
Aqua (Ultima Weapon Equipped)
All in all, the Ultima Weapon isn’t just one of the most awesome-looking keyblades in the game (especially when equipped by Aqua), but it is also a very good weapon choice for all three characters!
