The story begins when Rena moves back to Hinamizawa. Mion and Rena quickly become friends. The story chronicles the series in-between Rena moving back and Keiichi moving to town, with emphasis on the budding romance between Mion and Rena. When a new boy, Keiichi, moves to town, the relationship between Mion and Rena begins to change.
Th story has a sequel oneshot called denouement that goes more into depth on Keiichi, Mion, and Rena's relationship.
This fanfic provides examples of:
- Arranged Marriage: It's mentioned likely that Mion will likely be forced into an arranged marriage because she's her clan's heir. She realizes this but still wants to Marry for Love instead.
- Continuation: Both oneshots are set post-series, but denouement puts emphasis on the fact. It starts at the Watanagashi after the series ended.
- Holding Hands: Mion and Rena hold hands a lot. When Rena chastises Mion on not wearing gloves in the winter, she kisses her fingers and Mion decides on not wearing gloves for sure.
- Meaningful Rename: It's mentioned early on that Rena's birth name was "Reina". After correcting her teacher about her name, it's not mentioned again and everyone calls her "Rena".
- Polyamory: Though they're not an official couple at the end of Surprising Butterflies, the story is themed around the romantic feelings between Mion, Rena, and Keiichi. It starts out just Mion and Rena until Keiichi moves in. Despite their feelings for each other, both girls also like him and Keiichi becomes drawn to the duo as well.
- Platonic Kissing: Discussed when Mion is confused on whether Rena's kiss was platonic or not.
- Ship Tease: There's some Rika/Satoko teasing in denouement.
- Stepford Smiler: Mion, Rika, and Rena in particular are noted to have Stepford Smiler traits. Upon talking to Rena for the first time, Mion noticed her smile was hollow because she knew of Rena's Dark and Troubled Past.
- Twin Switch: Mion and Shion's switchings are mentioned, specifically when Satoshi was still around.
- Wise Beyond Their Years: Deconstructed with Rika and Mion. They were forced to grow up too soon and never felt they had the chance to act like children.