Bizarre Love Triangle

Plot Synopsis

High-schooler Yano Shiki falls in love with his classmate Minase Akiha after just one conversation, enchanted by her recitation of a poem he loved but was ashamed to admit he knew. But upon finding her in an empty classroom after school, he immediately noticed something was off... despite having the same face and attempting to pretend, she wasn't Akiha. With a little convincing, Haruka opens up and tells him the full story - that she and Akiha are two people in the same body who switch roughly every two hours, pretending to be one in the hopes that someday they really will merge back together. Convinced of their story, Yano offers to help Haruka successfully pretend to be Akiha, in return for Haruka helping him get closer to Akiha.

How is it plural?

Akiha and Haruka are explicitly stated to be "split personalities", formed at around the correct point in childhood for DID to occur. While it is never explicitly stated in the manga what the trauma was that caused them to split, they do not share memories and use notes to exchange information, hence requiring Yano's help to cover for the gaps in Haruka's memories and mannerisms when masking as Akiha. The story also touches on the topic of fusion, as Akiha and Haruka desire to fuse despite being advised against it by their family and doctor.