Kobeni is your typical, completely normal high school girl. She plays sports and lives with her freewheeling mother and her older, eccentric sister, Benio. Due to an accident when she was young, Kobeni can’t remember her childhood at all. Will she be able to remember her past? Are the people who want to become a part of her future really even people? Find out in Engaged to the Unidentified!
Kobeni has been married off at the tender age of 16 to honor her grandfather's wishes. Not only is her "fiance" moving in with her family, but he's bringing his little sister along with him. Or is it the other way around?
Mashiro becomes terrified of the thought of alien abductions. Benio continues to torment Mashiro with her love.
Benio and Kaguya get to know each other a bit more as they take a trip to the grocery store. Later, Mashiro and Kaguya get a letter from back home, and Benio learns more about her past with her new fiance.
Mashiro finds out about Kobeni's low constitution. Kaguya's speedy escape from a stressful situation leads Benio to question who he really is.
Mashiro and Kaguya's mother comes to Kobeni's house to visit. Things get a little strange when the new guest reveals what her family truly is.
Kobeni is becomes curious of Mashiro and Kaguya's other forms, but Kaguya refuses to transform in front of her. As Valentine's Day nears, Kobeni's mixed feelings towards her fiance to be have her worried.
The student council secretary, Suetsugi, has a tiny crush on Benio. In an attempt to get closer to her, she starts to suspect Mashiro and Kaguya's real identities.
Kobeni, after learning of Konoha's true identity, decides to keep it from Benio. Later, Mashiro and Konoha get to know each other better.
Even though Hakuya is a man of integrity and agrees to keep the engagement a secret, word gets out and soon everybody knows about his secret.
With the secret out, Kobeni attempts to set right the misunderstandings about the engagement to Konoha.
Looking to make up for missing White Day, Hakuya is torn on what gift he should get for kobeni.
After Hakuya and Mashiro's sudden disappearance, Kobeni sets off on a search for any sign of where they may have gone to but finds herself in quite the predicament.