Long-arm Centipede Sen'un is the nest mini boss fight in Sekiro, found in the game's Senpou Temple area, following on from Armored Warrior in our walkthrough of the game's bosses and mini-bosses.
You'll find Long-arm Centipede Sen'un inside a building down on the bottom right side of the area with a hole in one side of its roof, if you continue onwards and keep hanging right from the Senpou Temple - Temple Grounds idol.
Below, we'll cover how to beat Sekiro's Long-arm Centipede Sen'un, including any particularly strong methods or weaknesses they might have and any handy things to bear in mind.
For more guides and pages like this, meanwhile, cycle back to our main Sekiro walkthrough and boss guide hub.
Sekiro Long-arm Centipede Sen'un - how to beat and kill the first Long-arm Centipede
The first of two Long-arm Centipede bosses you'll face, Sen'un takes a bit of brief setting-up first if you want to beat it easily, but it'll make a real difference and won't take long.
How to set up Long-arm Centipede Sen'un
Enter the building where the monstrosity is waiting and stay on the rafters above it. Pick off all of the smaller centipede-people up there, and then drop down and pick off the rest on the bottom floor as quickly and safely as possible - remember you can grapple up and down from the rafters quite easily to help you get out of any corners.
There are a couple the other side of a panel that blocks the ground-floor exit from the building, too - when they're dealt with, hide from the Long-arm Centipede Sen'un until you lose aggro, and then go back up onto the rafters - stealthily - and drop down to land a free Deathblow for one of its two marks.
How to beat Long-arm Centipede Sen'un
Now, it's just a case of doing two things: deflecting every attack, and jumping on Sen'un's head when it does its Perilous Attack, which is always a pimcer-like swipe with both arms, and always a Sweep attack.
Looking for more Sekiro pages like this? First up, the first main Sekiro patch notes for update 1.03 are live. Otherwise, our Sekiro boss guide, boss list and walkthrough hub has everything in one place, including pages on Lady Butterfly, Genichiro Ashina Way of Tomoe, Folding Screen Monkeys, Corrupted Monk, Guardian Ape, Great Shinobi Owl, Emma and Isshin Ashina, True Corrupted Monk, and Divine Dragon. We also have in-depth pages like Sekiro tips and tricks to get you started, Sekiro Skills, skill tree and Esoteric Text locations explained, our deep dive on the Sekiro combat system, Posture, and Perilous Attacks, or details on all Sekiro Prosthetic Tool locations, how to cure Dragonrot and Rot Essence in Sekiro, Gourd Seed locations, a Divine Confetti farm route method, all Treasure Carp Scale locations, all, Prayer Beads locations and all Snap Seed locations, too. And when you're ready - the how to beat Isshin Sword Saint and an Isshin Sword Saint cheese, plus the many Sekiro endings.
If you like, hold down block to first time it does a flurry of attacks just to get the rhythm, and grapple up to the rafters to let your Posture recover, but then one way or another you're going to need to get parrying.
Face it head on, don't bother touching the dodge button, and just try to deflect every attack in its cycle. Be ready to jump when you see the red Perilous Attack symbol, for some hefty Posture Damage, and repeat that once or twice and the Long-arm Centipede's Posture bar will likely already be full, ready for you to finish it with a Deathblow - job done!
If you're really struggling, you can also cheese it, to an extent, by hopping up and down from the rafters for one aerial hit at a time, but it's honestly not worth the effort. Just keep cool, focus on sound and timing instead of how intimidating the centipede looks, and it'll go down easy.
That's all you'll hopefully need for tackling this encounter. Next up in our guide is Folding Screen Monkeys, or you can cycle back to our main Sekiro walkthrough and boss guide hub for much more explainers and advice.