Co-op
Sephiria supports online co-op for 2 to 4 players over Steam lobbies. The game labels the mode experimental and warns about crashes and sync issues, but the full loop works: shared runs, revives, mid-run rejoins and per-player progression.
Starting a lobby
The host creates a Steam lobby from their own town and the party gathers in an assembly area before the run starts. Lobbies come in three privacy modes: public, private, and private invite-only. Friends join through a Steam invite (accepted from the title screen) or by entering the lobby code directly, and the host sets the member cap between 2 and 4. Once a lobby has started exploring it locks, so latecomers can't drop into the middle of a run they weren't part of.
The host's machine runs the whole simulation; everyone else connects peer-to-peer through Steam. Expect the host to have the smoothest experience.
Who can join
Multiplayer isn't available from a fresh save: the game unlocks it after you complete the first death event in the story. Everyone must be on the same game version, and you can't join a host whose main quest progress is further along than yours. Some story beats block multiplayer entirely, and certain chapter steps must be finished in town before the party can move on (the game will name the player who still needs to talk to the Tree). Quick travel is disabled during a multiplayer game and the training room is single-player only.
Moving through a run
The party moves as a unit. Advancing to the next area requires everyone to gather close together; any player can request the move and the others see who asked. Only the host picks side missions, and quest board objectives have to be completed before the group can leave the floor. Dialogue choices are broadcast, so the party sees what each player answered.
Death and revives
A downed player isn't out of the run. Another player can revive them, and the interaction is explicit about the price: the reviver shares 50% of their own HP. Reviving takes time, and some effects shorten it (there's a dedicated "reduces the time to revive another player" status). The base revive timer is a per-character value the extracted data doesn't expose, so we can't quote a number for it.
Disconnects and rejoining
If someone drops mid-run, the game preserves their items and EXP so they can reconnect into the same floor. On relaunch the game detects the interrupted lobby and offers a rejoin; declining pays out the sapphires you earned in that session, so a crash doesn't cost you the meta currency. Hosts can kick players, and kicked or banned players can't rejoin that run.