A sudden system crash shatters the peace of ALfheim Online as Kirito, Asuna, and Alice enjoy a quiet moment at Kirito's log cabin on the 22nd floor of New Aincrad. The floating castle begins to disintegrate and fall, forcing the trio to use their wings to steer the debris toward a river below to break their fall. When they surface, they discover they are no longer in ALO but have been forcibly logged into a mysterious and brutal new VRMMO called Unital Ring.

This new virtual world is the result of a fusion of all VRMMOs built using The Seed program. The game operates on survival mechanics far harsher than anything the players have experienced before. All of their high-level equipment and stats have been reset to level one, leaving Kirito with only his most treasured sword and a pair of pants. The familiar menu interface has been replaced with a circular design, and new status gauges appear alongside health and mana. Even the logout function remains available, easing the immediate fear of another death game, but the stakes remain high as death in Unital Ring results in being locked out of the game permanently.

The group quickly discovers that Yui, Kirito and Asuna's AI daughter, is unable to manifest, and their friend list has been completely wiped. While most skills and proficiencies are reset, Asuna is relieved to find that Mother's Rosario, the original sword skill passed down by the late Yuuki, remains in her possession. As they struggle to navigate the unfamiliar forest and rebuild their destroyed cabin, they encounter another player named Mocri, a dagger sorcerer who becomes a crucial ally in understanding the rules of this new world.

The narrative follows Kirito, Asuna, and Alice as they adapt to starting from nothing, learning to craft basic tools and hunt for materials in an environment where even wielding a powerful sword can crush the wielder due to weight limit mechanics. The story explores not only their survival but also the grand mystery behind the emergence of Unital Ring and the secrets still hidden within The Seed. Alongside familiar companions like Leafa, Silica, and Lisbeth, the group must uncover why this game has appeared and who or what is behind the merging of the virtual worlds.