Sekiro is already an incredible single-player experience, but sometimes even battle-hardened players feel like they could do with some backup.
Enter Sekiro Online, a mod for the PC version of the game which adds both co-op and PVP features to the game (via DSOGaming). Mod author LukeYui explained they tried to make the online mode as similar as possible to the Souls series' online features, although it's obviously not quite as smooth - seeing as it started as a pet project and is still in early public beta.
Running through P2P connections rather than a central server, Sekiro Online can support up to six players, with one player hosting and the other five appearing as phantoms. Along with co-op and PVP the mod also adds the Souls series' invasions feature, which allows the player to enter an unsuspecting player's world "as a spirit of vengeance" to fight to the death. To add some balance to this, invading players and phantoms will be adjusted to the player's local level, otherwise things would get a bit unfair if an advanced player came in to repeatedly whack you. Although I guess that would be fitting for Sekiro.
LukeYui has released a couple of videos demonstrating how the mod works, and so far, it looks pretty impressive - although I feel the PVP might be hard to master purely due to the speed of fights and the inability to learn another player's attack patterns.
While you can play online anywhere in the game, sessions end every time you change areas, so there may be a bit of faffing required to rejoin between these. LukeYui also recommends waiting until after the tutorial area before trying online play, as "it can bug out and softlock you". As network progress is synced, a boss killed by another player will also die in your world - but some features seen in the Souls games (such as bloodstains) could not be implemented without a central server.
If you want to try out this mod with friends, each player will have to install the mod (the download and instructions for which you can find here), start a new save, and then either create or invade a session using the special items provided by the mod. Co-op requires the host to create a session, and then invite players through the Steam friends list. As with all mods, I'd probably recommend backing up any save files you want to keep safe before starting the installation process - just in case.
While it may not be the perfect online experience, it's still pretty impressive work, and seems like it would be a fun way to re-experience Sekiro with friends. LukeYui intends to keep improving and updating the mod, and I can't wait to see where this ends up.