Arknights Yesterday's Sea Stage Guide: Clementsa, Travelbone and Week-One Sanity Planning

Applicable version: as of the 2026-10-09 update (Arknights has no version-number system; the official announcement date is the anchor)

Arknights Yesterday's Sea overview: event dates and banner

Yesterday's Sea is a limited side story in the October slot. Hypergryph posted the teaser on 2026-10-03 and the event opened with the version update on 9 October at 12:00, with the shop running to 30 October at 03:59 so there is a window for extra farming after the stages end.

Event and banner timeline

Item	Time	Note
Version maintenance	2026-10-09 06:00	Stages open after it
Event stages	From 10-09 12:00	Clear first-time rewards first
Abyssal Cruise banner	10-09 12:00 to 10-23 04:00	Six-star Clementsa takes 50 percent of six-star pulls (source: official announcement)
Event shop	10-09 12:00 to 10-30 03:59	Travelbone tokens, furniture, permits

How to get the free operator Travelbone

Travelbone is the free five-star Specialist of this event, on the Alchemist branch, dealing sustained area damage through alchemy units; no gacha required, just play the stages and unlock the shop exchange . For players new to Arknights, pair this with a beginner guide and read Arknights beginner guide basics first, since the team logic in this Arknights guide builds on that.

Arknights Yesterday's Sea stage mechanics

The difficulty is not single-target power but spawn rhythm: wave-based pushes mean the same lane repeatedly takes ground and air pressure, so clear speed matters more than burst.

Wave pressure and air control

Air units usually arrive offset from ground units, leaving only a few seconds between them. A high-ground damage dealer that covers one target will leak on the second wave, which is why a group Caster beats a single-target Caster here .

The three-tier deployment

Put a high-block Defender at the front to stop melee and absorb wave one, a damage Dealer mid-lane for medium units, and a sniper plus group Caster on the high ground to clear and pick off. The benefit is concentrating slots on high-ground damage that covers ground and air .

Arknights Yesterday's Sea clear teams

Team	Line-up	Roles	Substitutes
Budget	High-block Defender, group Caster, sniper, two healers	Defender holds wave one, Caster clears groups, sniper picks off ranged	Any Elite 2 Defender or lower-tier group Caster
High-end speed clear	Two high-ground dealers, strong Dealer, single-target burst	Front-loaded damage to cut each wave's clear time	Swap by roster
No-pull starter	Travelbone, group Caster, two healers	Free operator fills the gap	Good for a fresh account in week one

Budget versus high-end

The budget team works if the Defender holds; as long as wave one does not leak, the Caster grinds the rest down. The high-end team front-loads damage and removes the toughest unit of each wave first to shorten field time .

Substitutes

With no high-end sniper, any Elite 2 high-ground dealer works, since the stage demands less burst than clear speed . Bring two healers: under two-lane pressure one healer gets focused .

Arknights Yesterday's Sea: building Travelbone and modules

Travelbone is a free operator, but the Alchemist role fits this event's clear needs, so if you are only going to build one free operator, pick it .

Role and skill priority

Travelbone deals sustained area damage and control through alchemy units; take the main skill to Level 7 and Elite 1, which is enough for the event and daily play. Level 7 is the stopping point because this event cares about skill frequency, not panel numbers (source: hands-on testing).

Module priority

New modules in the same update include the De Toledo Y module (Skill SP recovery +0.25 per second while an elite or leader enemy is in range) and the Travelbone X module (Skill SP recovery +0.1 per second while an alchemy unit is on the field) . Both speed up skill cycles, so unlock them first if your team stalls in skill downtime.

Arknights Yesterday's Sea resources and Sanity planning

Window	Sanity goes to	Originite handling	Reason
Three days before	Bank above 1,200	Claim, do not spend	Room to grind in week one
Week one	First clears and fixed stages	Depends on banner	First-clear rewards are not to be missed
Week two	Material stage farming	Keep an 1,800 buffer	Covers a mid-month second banner

Week-one Sanity

At roughly 240 Sanity of natural regen per day, banking three days early frees about 720 extra Sanity for the event . Clear every first-time reward first and only then farm material stages, because first-clear value clearly beats repeat farming .

Originite and banner trade-offs

Locking one banner, at 6,000 Originite per ten-pull, needs a reserve of 18,000 or more to be safe . With limited resources, chase only the Clementsa banner and move the rest into operator building. Other games running in the same week can be lined up against the guide hub at gghubs.com so stamina does not spread too thin.

Arknights Yesterday's Sea FAQ

When does Yesterday's Sea open?

A: 2026-10-09 at 12:00, with the shop open to 10-30 03:59 and maintenance starting at 10-09 06:00 .

How much Sanity should I bank before the event?

A: Bank more than 1,200; at about 240 a day, starting three days early frees roughly 720 extra .

Which operators should I build first?

A: A group Caster and a high-ground sniper, both at Elite 2, with 18 or more mid-to-high tier promotion materials each .

Arknights Yesterday's Sea action checklist

1. Bank more than 1,200 Sanity before launch and only claim Originite.
2. Clear first-time rewards before farming materials; do not reverse the order.
3. Use the three-tier deployment of blocker plus two high-ground dealers.
4. Take Travelbone to Skill Level 7 and Elite 1, and unlock the X module first.
5. Reserve 18,000 or more Originite if you lock a single banner.