After being trapped in the world of Elder Tale for six months, Shiroe and the other Adventurers have begun to get the hang of things in their new environment. The Adventurers are starting to gain the trust of the People of the Land, and Akiba has flourished thanks to the law and order established by Shiroe's Round Table Alliance, regaining its everyday liveliness. Despite this success, however, the Alliance faces a new crisis: they are running out of funds to govern Akiba, and spies from the Minami district have infiltrated the city.

As formidable forces rise in other districts, there is also a need to discover more about the vast new world they are trapped in—leading Shiroe to decide that the time has come to venture outside the city. Accompanied by his friend Naotsugu and the Sage of Mirror Lake Regan, the calculative Shiroe makes his move, hoping to unravel new possibilities and eventually find a way home.

One day, while playing the online game Elder Tales, 30,000 players suddenly find themselves trapped in another world. There, eight-year veteran gamer Shiroe also gets left behind. The trapped players are still alive, but they remain in combat with the monsters. The players don't understand what has happened to them, and they flee to Akiba, the largest city in Tokyo, where they are thrown into chaos. Once proud of his loner lifestyle, Shiroe forms a guild called Log Horizon with his old friend Naotsugu, female assassin Akatsuki and others.

In the blink of an eye, thirty thousand bewildered Japanese gamers are whisked from their everyday lives into the world of the popular MMORPG, Elder Tale, after the game's latest update—unable to log out. Among them is the socially awkward college student Shiroe, whose confusion and shock lasts only a moment as, a veteran of the game, he immediately sets out to explore the limits of his new reality.

Shiroe must learn to live in this new world, leading others and negotiating with the NPC "natives" in order to bring stability to the virtual city of Akihabara. He is joined by his unfortunate friend Naotsugu, having logged in for the first time in years only to find himself trapped, and Akatsuki, a petite but fierce assassin who labels Shiroe as her master. A tale of fantasy, adventure, and politics, Log Horizon explores the elements of gaming through the eyes of a master strategist who attempts to make the best of a puzzling situation.

A gate to another world opens in Mikado City, and monsters called Neighbors emerge. It's up to Border Defense agent Osamu Mikumo to fight them.

A gate to another dimension has burst open, and from it emerge gigantic invincible creatures that threaten all of humanity. Earth's only defense is a mysterious group of warriors who have co-opted the alien technology in order to fight back!

The border defense organization "Border" was established to fight against the attacks of the "Neighbors" who possess unknown power. Osamu Mikumo, a member of the Border, forms the Mikumo Squad with Yuma Kuga, a Neighbor who he met by chance, and his childhood friend Chika Ametori, and they struggle to win the internal Border rankings in order to join the expeditionary force to the Neighborhood.

With Hyuse joining the Tamakoma Squad, the rank wars are continuing and the Tamakoma squad are striving to get selected for the Away Missions.