Moonlit Black Cats was a mid-level guild with relatively few members, although all of them, except for Kirito, knew each other offline as the guild was formed from the members of a school's computer club.
On April 8, 2023, Kirito assisted the Moonlit Black Cats when they were being pushed back by monsters in a Labyrinth while their only forward, Tetsuo, had suffered heavy damage and could switch places with anyone. While holding back on fighting the monsters, Kirito led the guild out of the Labyrinth, thus the guild invited him to an ale house to thank him. At the ale house/inn in Taft, the guild toasted for Kirito's help. During their conversation, Keita, the leader of the guild, asked Kirito about his level. Kirito lied about his true level, claiming it to be around the level of the guild members, when in fact his level was two times higher than the one claimed. Since Keita believed that Kirito was around their level and would be soon invited to join a guild, he invited him to join them. Kirito accepted the invitation, but planned to only remain as a temporary member until the guild became strong enough to be independent.
During the next couple of months, Kirito assisted the guild, especially Sachi, who was deeply afraid of death. During the time lapse, the members of the guild had hopes of being strong enough to catch up and join the Clearers on the front lines, and, with Kirito joining them, they believed they stood a chance of catching up.
On June 22, 2023, the guild finally acquired enough money to purchase a home for the guild, thus Keita left for the Town of Beginnings to bargain out for one. The other members then wanted to impress Keita by obtaining items from monsters stronger than them to earn money to celebrate their new home.
While exploring the Labyrinth of the 27th Floor, the guild came across a hidden room with a treasure chest in the middle of it. Ducker, whose trap disabling skill was too low, accidentally triggered a trap, causing the room to be sealed in an Anti-Crystal Area. Simultaneously, Granite Elementals and Dark Dwarf Miners, which were much higher in level than most of the guild members, quickly filled the room. The guild was quickly overwhelmed, resulting in all of them except for Kirito, who survived due to his higher level, to be killed. After Kirito informed Keita of the deaths of their fellow guild mates, the latter cursed Kirito's status as a Beater, before committing suicide by jumping off the edge of an Aincrad floor.
The members of the Moonlit Black Cats in real life (episode 3 end card).
After the death of his guild mates, Kirito treated a tree growing next to the inn that the guild once used as a headquarters as a replacement for a grave for the fallen guild. He continued visiting the site occasionally.