Sweet Souls

Tigerlilly is a very old, powerful and knowledgable Shinigami. She is a hardworking despite the other's laziness.
One thing though. She's extremely humanoid but still possesses the qualities of a Shinigami. She doesn't mind, but wears a mask to hide some of the humanity in her in case others confuse her for human.

Tigerlilly enters the human realm to investigate the sudden deaths around, no doubt caused by a Death Note. She finds L, the main brain behind the police investigation, intriguing due the fact he finds a logical explanation for everything. She stays there, doing her job and watches over the life of L and Light Yagami, another intriguing human.

What will happen?