LegendarySword

Rengoku

Weapon · Blox Fruits

🌊

Seas

📅

Update

#13

How to Obtain

Use Hidden Key

📍

Location

Ice Castle

Description

Hidden deep within the Ice Castle, Rengoku is a legendary sword that demands genuine effort to obtain — you need a Hidden Key to unlock it, making it one of the more coveted finds in the Second Sea. Because it sits in the legendary tier, it hits considerably harder than common or uncommon blades, and its power scales with your Sword stat as you raise it through mastery. The sword's two moves, Demon Slayer and Burning Slash, give it a fiery identity that sharply contrasts with its icy surroundings. Burning Slash in particular rewards aggressive, close-range playstyles, while Demon Slayer adds a dash of area pressure to the kit. Rengoku is a strong pick for sword mains who have progressed far enough into the Second Sea to actually reach the Ice Castle. Farming mastery on it consistently will unlock its full damage potential over time.

Moves & Abilities

3 moves

Normal Attack

The player does 3 slashes, then performs a lunge on the fourth.

Demon Slayer

✨ Mastery 150

The user dashes forward, leaving a trail of orange and red flames. If the user hits an enemy, the user slashes the enemy rapidly and finally releases three fire-like slashes, dealing tick damage with a burn effect. The burn lasts for around 2 seconds.

Burning Slash

✨ Mastery 350

This move offers two distinct variations: * If tapped: ** The user releases a horizontal slash of flame, which leaves a trail of flame on the ground. If the slash hits an enemy, it damages them and causes burns that cause tick damage over time. * If held: ** The user's screen will first turn red like flame, then releases a huge wave of flame that deals widespread damage. Deals tick damage over time, similar to the tap variation.

Pros

✦Extremely high damage.
✦Good combo potential.
✦Good knockback, which is useful in PvP.
✦Both moves break Instinct.
✦Insane damage in short duration, making Shark and Cyborg users take a lot of damage before they can turn on their Race ability.
✦Dash is very fast.
✦Almost no end lag.
✦Can target multiple players.
✦Damage is still dealt as long as the target has been caught in the dash (Unless "Instinct-Tricked").
✦Deals damage over time.
✦Good range.
✦Can stun Blade users along with Saishi.
✦The flames break Instinct.
✦Breaks Instinct on direct contact.
✦Decent AoE when held.

Cons

✦Cannot damage Blade users.
✦Low drop chance for the Hidden Key.
✦Bad for in-water combat.
✦Difficult to grind due to dashing from the fourth slash.
✦High mastery requirements.
✦Single target. (Though the flames can damage nearby enemies if they are close)
✦The flame trail can be dodged easily if not stunned.
✦This move, along with its two variations, does not have any AoE burn when used aerially, making it significantly harder to hit (the tap variation works similarly and has a similar hitbox to awakened Dark's , the held variation works the same, just vertically).

Trivia

1Rengoku is an easter egg that the devs added at Update 13.
2Before the rework in Update 20, did not do burn damage.
3Rengoku's moveset post-rework is similar to the Pipe.
4Rengoku is the only katana to be out of its hilt in its icon.
5can sometimes glitch the player out of the map if the flooring is thin like in Kingdom of Rose.
6Rengoku's passive idle stance was revamped again.
7Rengoku's model was revamped.
8Rengoku's damage was nerfed.
9Rengoku's moves were reworked.
10Added burn damage to [Z] Demon Slayer.

More Swords

Rengoku — In-Depth Analysis

What Is Rengoku?

Rengoku is a Legendary sword hidden behind the Ice Castle in the Second Sea, unlocked by using a Hidden Key. The low drop chance for the Hidden Key is a known barrier, but the payoff is one of the most damage-efficient swords available in the Second Sea — Rengoku is widely regarded as a top-tier Second Sea blade for good reason.

Why Rengoku Stands Out

Rengoku's core identity is overwhelming burst damage delivered via a fast dash that deals damage over time through fire-based lingering flames. The dash speed is exceptional and produces almost no endlag, creating a window where you can chain follow-up attacks before the opponent recovers. Both moves break Instinct — on direct contact and via the flame trail — which is critical against Instinct-reliant defensive players.

- Exceptionally high burst damage with damage-over-time flames - Fast dash with near-zero endlag — excellent combo flow - Both moves break Instinct, including the flame trail - Can stun Blade users alongside Saishi (uncommon cross-immunity bypass) - Good range and multi-target potential when enemies are close together

The weaknesses: Blade users are otherwise immune, the Hidden Key's low drop rate makes obtaining it genuinely frustrating, and the flame trail's aerial version has a noticeably smaller hitbox. Rengoku also underperforms in water.

Tip: Chase the Hidden Key actively — defeat Ice Castle enemies repeatedly until it drops. Once you have Rengoku, lead combos with the dash move to proc Instinct-break and DoT simultaneously, then layer your fighting-style moves into the burn window.

Where it shines

Extremely high damage.
Good combo potential.
Good knockback, which is useful in PvP.
Both moves break Instinct.
Insane damage in short duration, making Shark and Cyborg users take a lot of damage before they can turn on their Race ability.

What to watch out for

Cannot damage Blade users.
Low drop chance for the Hidden Key.
Bad for in-water combat.
Difficult to grind due to dashing from the fourth slash.
High mastery requirements.

How to Get Rengoku