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