I'm a proud DS owner because I love old school JRPGs, and there's so much to love on the DS.
Right now I'm playing Luminous Arc 2, which is a Tactical RPG. The main character is a Squire named Roland, who quickly becomes the first Rune Knight in 4000 years. He gets his magic powers by joining with Witchs. At first, the joining is just an exchange of a ring and magical energy. Later in the game, a deeper form of engagement is introduced that involves a kiss and a vow to serve and obey.
Basically, the plotline of the game is a guy and his harem of beautiful witches set out to save the world. It's actually a lot of fun.