It's not Sunny's fault. It's never Sunny's fault. The shadow made him do it.
All Basil has to do is kill it.
The end of the game told from Basil's perspective.
"You must want to save me," Basil smiles faintly and plays with his flower crown, "or maybe you just want a reason to see me."
This fic takes place after the good ending of the game.