If you were to bring Kid out of her coma with the Chrono Cross, you could play with her... (I should be careful how I say this) for the rest of the game. No, she doesn't become the love of Serge's life. Buggar! Serge ends up going back to the Opassa Beach at moment he passed out beside Leena and to him the whole adventure seems like a dream. He and Leena spend the whole summer together. End of story. I like Leena, but I think it would have been cool if Serge had forgotten his promise to her and went after Kid... but only at the end of the game.