It's a NaLu. It's about Lucy getting stronger and about finding new keys as stated in the cover. Also this is the first book in The Lost Keys series.

Elizabeth Liones, The Third Princess of the Liones line; she has trouble in her studies because of running away from her peer problems. Some of the guys gawks at her - not for her looks but her personality and brains. Especially not for her large bust. That's the reason why a lot of females dislike her. Sometimes they even get jealous. She's the former President of the Creative Writing club. She totally outshines the others in her class. Practically, she's smartass. Meliodas, the hearthrob of the St. Chronica's Academy. Even some guys stops being straight for him. He's the current Captain of the Football team, he has quite a hard time in keeping up with his academics. He's a dumbass obviously and a pervert. But he has a soft side, which a lot of people are not aware of. He thinks every girl in the world are the same, ever since he lost the love of his life. Until they crossed paths, how will she affect Meliodas' life when she enters the spotlight? Could she be the one to change him?