I had this really cool dream last night.
So Lumine's a college student, right? I dunno what she studies. And there's a serial killer going around campus. The first victim was Signora. Childe is a transfer student from another college - one much more advanced than Lumine's. So when he makes a presentation on a gravity distortion device he and a few friends (probably Arlecchino and Dottore) everyone is blown away.
Later, at a bar, Kuni teases Lumine about how bad she has it for Childe (she doesn't, but they're best friends). Childe creeps up behind Lumine and startles her. He buys her a drink and Kuni leaves, smirking. They talk for a while, and Childe invites Lumine to visit his college, saying she's too good for this place. She declines and goes home. The next day, Ayaka, a girl Lumine had a crush on, is dead.
Lumine decides to start looking into the murders. She seeks counsel from Childe, who just wants to make time with her. He does tell her that maybe Lumine is the target, seeing as she liked Ayaka and Signora was her least favorite teacher. Lumine considers this and heads to a cafe with Kuni. On her way, she spots someone fighting in an alley. Kuni runs in to break it up and chases a hooded figure away. The other person was Lumine's brother, Aether. There's a knife in his shoulder.
Lumine's on the verge of insanity at this point. Kuni's doing everything he can to help her, but to no use. All he can do is tell her how much he cares about her. The next morning, his dismembered hand is hanging on her door. Lumine can only think of one person at this point: Childe.
Lumine marches over to Childe's hotel and demands answers. He says he'll tell her, but not at the hotel. They head to a ferry and Lumine starts asking why. Childe denies having any part in the murders. But then, he starts speaking strangely, and presses a button on his phone. Water starts winding around the ship. It turns out that the gravity distortion device he showed in class was just a prototype. The real one was the boat.
"Signora asked too many questions."
"Ayaka stole your attention from me."
"Kuni got in the way."
Lumine couldn't believe it. She snatched the phone and pushed Childe over the side of the boat.
A year later, Lumine is in Snezhnaya visiting Tonia and Teucer. Tonia knows the whole story, but Teucer thinks his brother is just taking a long vacation.
To this day, Lumine can't bring herself to tell him.