Kaguya Houraisan is a brilliant sheltered beauty who lives in hiding at Eientei. She is a Lunarian, a person of Hourai, and a princess. However, she is just another ordinary student at Hakurei Shrine Academy. No one was surprised when they saw Kaguya's mischievous grin as she watched Mokou rush into class just as the morning bell chimed.

Fujiwara no Mokou is a fiery and solitary student. She is a human skilled at youjutsu, a person of Hourai, and a maiden who dances like a phoenix. However, she is just another ordinary student at Hakurei Shrine Academy. When she pulled back her seat to sit down, a flood of love letters spilled out of her desk. The bold and valiant Mokou has many admirers. She cringed in exasperation as she carried the mountain of letters out of the classroom for the hundredth time.

Keine Kamishirasawa is a wise and intelligent trainee teacher. She works as a teacher at the school in Gensokyo, and she is also a teacher at Hakurei Shrine Academy. The textbooks might be different, but the pain the students feel from her headbutt punishments is the same. She watched Mokou leave the classroom in silence, but she could predict what was going to happen next, so she scowled at Kaguya and warned her not to go overboard.

Within the pile of love letters from Mokou's admirers, there was one letter that stood out. It was a letter challenging Mokou to a duel sent by Kaguya Houraisan. At first, Mokou was surprised since she was the one who usually issued the challenges, but then she realized that hiding the challenge within a pile of love letters was just another one of Kaguya's pranks. Mokou shook with anger and excitement for the battle to come as she clenched the letter of challenge in her fist and walked around to the back of the school.

Kaguya burst out laughing as soon as she spotted Mokou, who came to answer her challenge. She explained that the fact that Mokou found the single letter of challenge within that huge pile proves that Mokou considerately reads every single love letter. Mokou's face went bright red in response to Kaguya's jeering laughter. This set the stage for another peaceful battle to the death―a common occurrence in the daily life of Hakurei Shrine Academy.