Lilly is second in command of team Yin-Yang. They are among the schools bullies. Yin-Yang was started by Helia who insisted on finding other dual-types like herself. Lilly fits the bill, being a Grass/Flying type.
Lilly will sweetly invite you to tea and then just as sweetly poison your drink. She likes having power and likes manipulating people. She prefers to use the rules to her advantage, finding loop-hole or clauses that allow her to inflict the most amount of harm on a person she can. She's not above getting new rules made that will give her more power.