AtsuLucy

AtsuLucy is the ship between Atsushi Nakajima and Lucy Maud Montgomery from the Bungou Stray Dogs fandom.

Canon
Atsushi Nakajima and Lucy Maud Montgomery first meet after Lucy has trapped members of the agency inside her ability, Anne of Abyssal Red, which makes her able to bring people into a separate reality called Anne's Room, where they're trapped until she lets them leave.

She traps Atsushi and Tanizaki Junichiro in the room and challenges them to a game of tag, where if they win she'll let the agency members go. They agree, and Tanizaki is immediately caught due to Anne's speed. Atsushi is able to evade, and he eventually gets to the door where everyone is trapped. As he's about to use the key, however, it tries to attack him, and Lucy explains that not even she knows how to use the key and only Anne could open it.

Atsushi, who realizes the whole game was a trap, tries to run, but is stopped by Ougai Mori, who reminds him that if he leaves he will have no memory of the room, leaving everyone still trapped in the room. Atsushi goes on the offense, but is soon caught by Anne, and is pulled into the room. Lucy celebrates momentarily, but then she realizes that at the moment the door opened, Tanizaki activated his ability, creating the illusion that Atsushi had been pulled into the room when in reality he had been holding onto the door frame to keep himself from being pulled in. Lucy then realizes that Atsushi had also tied a ribbon around her waist, and he pulls her towards where he is, grabbing her. He explains to her that he's going to let go, and she'll have a split-second decision to let everyone free from the room, or be trapped in her own reality until she dies, along with everyone else. Atsushi lets go and Lucy screams, deactivating her ability, making everyone that was previously trapped in the room reappear in the street where she had forced them into her reality. Atsushi goes to say something to Lucy, but she runs away, crying because she had failed her mission from the Guild and was now facing certain doom. Later on, Atsushi has been captured by the Guild, and as he's being held in a cell, Lucy comes to taunt him and tells him about what her time in the orphanage was like, showing him scars on her arm from when she was poked with a hot metal rod. Atsushi empathizes with her and shows her his own scars from his orphanage on his ribs. Lucy then brings him into Anne's room, giving him a parachute and telling him that if he exits the door he'll be right outside the Moby Dick, able to escape. He asks if she'll be okay, and she tells him that as long as she's in Anne's Room she'll be safe, and asks him to come and save him later when he comes back. Atsushi promises he will, and jumps off the Moby Dick.

After defeating the Guild, Atsushi goes with Kyouka Izumi to visit the Uzumaki Cafe, where they see Lucy walking in carrying a metal box. Atsushi asks what she's doing there and Lucy throws the metal box at him, yelling and blushing. They later find out she works there, and Lucy aggressively serves Atsushi and Kyouka some water and gives Kyouka a dispatch about her parents, and as they go to the shipyard to find where it is, they realize a page is missing, which Lucy took without their knowledge to get revenge on Atsushi. Lucy shows Atsushi that she has the paper, before crumpling it and throwing it into the water. Atsushi dives in after it, getting his leg caught in boat debris and he starts drowning, raising his arm out of the water for help. Lucy jumps in after him, bringing them both into Anne's Room as she complains about him being an idiot and drowning in such shallow water and how her work clothes are wet. Atsushi apologizes and comes up with an idea to have Lucy transport the moisture out of their clothes by bringing them back to reality then Anne's Room. Lucy says she isn't sure it will work but transports them back to reality, then snaps her fingers to bring them back to Anne's Room. As they enter Anne's Room, instead of just the water in their clothes being left behind, their clothes have been left in reality, leaving them naked in Anne's Room. They take a moment to process what's happened, and Lucy screams at the top of her lungs, sending Atsushi out of her reality.

Fanon
The ship is one of the more popular Het ships in the Bungou Stray Dogs fandom, mostly in part because of Lucy's hinted attraction to Atsushi and their interactions with each other hinting at a possible future relationship.

Fandom
Fan Fiction
 * Lucy Maud Montgomery/Nakajima Atsushi on AO3

Trivia

 * Lucy doesn't call Atsushi by his first name, but rather many varieties of cat-related nicknames.