Reiatsu Core is a legendary-rarity item in Sailor Piece that sits at the center of two major late-game progressions: Ascension 4 and the Aizen Sword. It drops exclusively from the Aizen boss in Hueco Mundo, and with a slim 3% drop chance, you'll almost certainly need to grind through multiple kills before one lands in your inventory.
Quick answer: Travel to Hueco Mundo, defeat the Aizen boss in front of the dome building, and hope for the 3% Reiatsu Core drop. Repeat every time he respawns. Boost your Luck stat to improve your odds.
Aizen Boss Stats and Spawn Location
Aizen is stationed in Hueco Mundo, directly in front of the large dome building. You can reach Hueco Mundo through the map portal, but keep in mind it's a late-game zone — you'll want to have completed earlier quests and leveled up substantially before heading there. Aizen has 25 million HP and respawns on a short timer, which makes back-to-back farming practical once you can handle the fight.
| Detail | Value |
|---|---|
| Boss name | Aizen |
| Location | Hueco Mundo (in front of the dome) |
| HP | 25,000,000 |
| Respawn timer | ~5–7.5 minutes |
| Reiatsu Core drop rate | 3% |
| Reiatsu Core rarity | Legendary |
Full Aizen Drop Table
Reiatsu Core isn't the only reward from this fight. Aizen drops a wide spread of items, most of which are far more common. Knowing the full table helps you gauge how many kills you'll need to stockpile materials for both the Aizen Sword and Ascension 4.
| Item | Drop Chance |
|---|---|
| Haki Color Reroll | 100% |
| Race Reroll | 85% |
| Trait Reroll | 75% |
| Boss Ticket | 45% |
| Dungeon Key | 30% |
| Mirage Pendant | 20% |
| Illusion Prism | 8% |
| Reiatsu Core | 3% |
| Manipulator (Title) | 2% |
| Aizen Haori (DMG +40%, DEF +50%, DMG taken −15%) | 2% |
| Hogyoku Fragment | 1.2% |
Because the Aizen Sword recipe also requires Mirage Pendants, Illusion Prisms, and a Hogyoku Fragment, extended farming sessions naturally build up those materials alongside your Reiatsu Core hunt.
How to Farm Reiatsu Core Efficiently
Step 1: Travel to Hueco Mundo via the map portal. Position yourself near the dome building where Aizen spawns so you're ready the moment he appears.
Step 2: Equip a high-DPS build or your strongest sword before the fight. The faster you bring Aizen's 25 million HP to zero, the more kills you can fit into each farming session.
Step 3: Stack as much Luck as possible. The Fortune rune, the Destiny Marked title, and the Kitsune race all raise your Luck stat, which directly improves drop chances. Combining multiple Luck boosts compounds the benefit.
Step 4: Fight in a group whenever you can. Multiple players burning through Aizen's health pool means quicker kills and a tighter farming loop. Have your skills and cooldowns ready before each respawn so damage starts immediately.
Step 5: Stay in the area between spawns. Traveling away and back wastes time that could be spent waiting at the spawn point for the next cycle.
Trading for Reiatsu Core
If RNG isn't cooperating, you can also acquire Reiatsu Cores through player-to-player trading. Because of the item's legendary rarity and low drop rate, sellers typically demand high-value returns. Use the in-game Trading option to open a deal, and always double-check both trade windows before confirming to avoid scams.
Reiatsu Core Uses — Ascension 4
The fourth Ascension tier requires four Reiatsu Cores alongside a Blood Ring (a mythical-rarity drop from Alucard at 2%). Beyond the material cost, you also need to meet several activity thresholds before the Ascensions NPC — modeled after Killua on Sailor Island — will let you proceed.
| Requirement | Amount |
|---|---|
| Reiatsu Core | 4 |
| Blood Ring | 1 |
| Use any ability | 500 times |
| Clear Shadow Dungeon (Medium) | 10 times |
| Defeat NPCs | 625 |
| Total damage dealt | 1 billion |
| Defeat bosses | 50 |
Completing the fourth Ascension grants stacking buffs: 10% more Gems earned, a 5% Luck increase, and a 2% reduction in cooldown times. These bonuses are permanent and layer on top of rewards from earlier Ascension levels.
Reiatsu Core Uses — Aizen Sword (Mythical)
The Aizen Sword is a mythical-rarity weapon obtained through the Aizen Trainer NPC in Hueco Mundo. You'll hand over materials first, then complete a five-part quest chain before the sword is yours.
Material cost
| Item | Quantity |
|---|---|
| Reiatsu Core | 3 |
| Mirage Pendant | 10 |
| Illusion Prism | 6 |
| Hogyoku Fragment | 1 |
| Gems | 10,000 |
| Gold | 6,000,000 |
Quest chain after turning in materials
| Quest | Objective | Notes |
|---|---|---|
| 1 | Defeat 250 Hollows | — |
| 2 | Unlock the Shinigami race | 1% chance per Race Reroll |
| 3 | Use a Worthiness Fragment | 25% chance this quest fails; retry if it does |
| 4 | Deal 350 million total DMG | — |
| 5 | Defeat Aizen 15 times | — |
Aizen Sword to True Aizen — Quick Note
The Aizen Sword is itself a crafting ingredient for the stronger True Aizen weapon, obtained from the True Aizen Trainer NPC at Soul Society. Only one Aizen Sword is needed for that recipe. Importantly, the True Aizen boss does not drop Reiatsu Cores, so there's no reason to fight that version if your only goal is collecting cores. The True Aizen boss is summoned with a Chrysalis Sigil and drops its own separate loot pool, including items like Fusion Ring, Divinity Essence, and Transcendant Core.
Between Ascension 4 and the Aizen Sword, you need a total of seven Reiatsu Cores. At 3% per kill, that's a significant time investment — but stacking Luck bonuses, running high-DPS builds, and grouping up with other players will compress the grind considerably. The respawn timer is forgiving enough that you can stay in one spot and loop kills without downtime, so settle in at the dome in Hueco Mundo and keep swinging.