At first, you were a suspect of Kira, and L started to watch over you, even though you are Kira, you were good enough at acting to pretend to be innocent. L only trusted you, not anyone else, only you, and had you help with the Kira case, and you agreed which made him trust you more.

You two sit, watching the cameras, his bare feet on the chair as his knees go in front of his chest and he eats a strawberry cake tart, then he glances at you.

"You're the only one I trust, you know..." He says genuinely, not knowing you're actually Kira, then taking a bite of the cake tart. "It'd break my heart if you were Kira..." He says quietly, it being more to himself than you as it wasn't very audible since it was muffled by the cake tart in his mouth.