The Two of Us Shall Waltz is the twenty-first episode of the Log Horizon anime. Unlike the other episode titles, it does not coincide with its corresponding light novel chapter because most of the episode was only briefly mentioned in the original source.
Shiroe is writing at one end of a long table, Akatsuki is kneeling at the other end, asking if he would attend the party. He responds that he doesn't like fancy events and would let Krusty handle the dialogue.
At the party, Krusty is in the center of a small group of Landers, being praised for the victory over the Goblin forces. He responds that it was teamwork between the People of the Land and the Adventurers that brought success. Princess Rayneshia watches this exchange with two ladies, becoming more and more agitated with each compliment given to him. Elsewhere at the party, members of the Crescent Moon Alliance are enjoying the food and talking to Nyanta, while several Lander children run looking for Akatsuki, the "Queen of Hide and Seek". Shouryuu mentions that it is too early for a victory celebration, but Nyanta explains the politics of the situation are vital even for the goblin defense: Now that Akiba and Eastal have political relations, the Adventurers have made it known that they are available for quests from the People of the Land. Marielle has just given Isuzu permission to leave the Crescent Moon Alliance so she can join Log Horizon. Henrietta is on the hunt for the no-show Shiroe, telling Nyanta and Naotsugu that it wasn't okay for him to be missing. Hearing Henrietta calling for him, Shiroe makes a hasty retreat into the night, leaving Akatsuki behind to fall into Henrietta's amorous clutches.
The Rise of Magic
Outside, Shiroe receives a call from Ooshima, informing him of the Demon Festival of Suzuka Gate in the west. On his way to consult with Li Gan, Shiroe hears a woman telling a story to a group of children. He is shocked to hear a retelling of how he transformed Rudy from a Lander to Adventurer to save his life, since it was supposed to be a secret. The mysterious woman finishes her story with a promise of more later, and vanishes into the shadow of an archway.
Shiroe is surprised when Li Gan congratulates him for creating a new World-class magic, who explains he felt (and observed) the power when it occurred. Li Gan adds that he has also felt the same power from the west, which Shiroe deduces to be in Minami. They recount the situation in Susukino, which had yet to recover from being taken over by Brigandia. In the months since Shiroe's Party rescued Serara, several armies led by Isaac had removed those who wished to leave Susukino, leaving around 200 adventurers still ruling over the city. Shibuya is abandoned in favor of Akiba, and a single guild rules over Minami, where the Demon Festival is currently underway. Li Gan adds that the Knights of Izumo had been involved in the west around this time.
Back at the party, a trio of adventurers are standing on the main staircase telling the crowd about the Goblin General battle, Nyanta and Naotsugu commented that the trio didn't know about the memory loss; as far as they knew, only key personnel on the Round Table Alliance have been told about the memory loss. Meanwhile, Shiroe, lost in thought, was found by Henrietta looking for him to bring back to the party.
As the Elder Tale theme plays, Krusty invites Rayneshia to dance in order to break the anxiety of everyone. As they dance, she remembers to a conversation between her and Serjiad Corwen. He tells her that she alone is responsible for the Adventurer's involvement in the war and the kingdom will not be providing any compensation to them, so she is fit to become the ambassador to Akiba. Krusty brings her out of her thoughts with his apparent mind-reading ability, saying being an ambassador isn't too bad, and she will be able to return to her lazy lifestyle. She imagines a life of leisure, but he brings her back with a comment on how she tends to sabotage herself.
Across the room, Serara tried to explains to Nyanta that no matter how much she wanted to, she wouldn't be able to join Log Horizon due to her duties in the Crescent Moon Alliance. He compliments her for making a wise choice, then asks her to dance, which she gladly accepts.
As Minori crosses the room, she hears dark rumors about Shiroe: how he manipulated Rayneshia, and how he shouldn't be in the Round Table Alliance. Shiroe and Akatsuki linger outside the party, with her now uncomfortably attired in a party dress. Akatsuki tells Shiroe how lately she has felt useless being unable to help him. Shiroe tries to comfort her, telling her that without her by his side through all he's done, he wouldn't have been able to accomplish anything.
Another dance round has begun, and Marielle takes Naotsugu onto the dance floor. Rudy also invites Isuzu to dance, after briefly seeing him as a cute dog, she accepts. Henrietta accepts a dance invitation from Serjiad Corwen. Finally, Shiroe asks Akatsuki to dance, although she hesitates, saying she doesn't know how to dance. He points out that she had been practicing before, and mentions he himself is clumsy at dancing. They dance offscreen, puzzled at their awkward movement.
Back in Akihabara
Several days later, Rayneshia is welcomed to Akiba with banners and cheering crowds. Shiroe exposes that instead of making an announcement about the loss of memory during revival, he spread the information in the form of a rumor. This prevented a panic, but some rumors suspect the Round Table Alliance had withheld the information, propagating more rumors about Shiroe that Minori picks up while shopping.
Later at night, she is reading her notebook on the roof of Log Horizon headquarters. Shiroe appears and asks if there is something he can help, she almost confesses her feelings, but instead asks about changing her skills.
The next day, several members of Log Horizon and Crescent Moon are partying at the Silver-Leaf tree. Henrietta, while coddling Akatsuki, explains how Marielle and the crafting guilds plan to hold an autumn festival that will include a debut fair of new products. Marielle states the festival will be in two weeks, making the others shocked at the short notice. She says not to worry, as she will be the strategist for the event as she mimes "Air Glasses". Finally, she announces the event will be called the Libra Festival.