Radiant Historia

A mysterious brother and sister bemoan their inability to save the world from being engulfed in sand...again. But they resolve to keep trying. Then the focus shifts to Stocke, a special intelligence agent who has been entrusted with the White Chronicle and sent on a high-stakes rescue mission. When the mission goes very badly, Stocke is able to use the White Chronicle to reach "Historia" and, with the help of the siblings, travel back to set right what once went wrong. Now, it's up to him to change history and prevent the Sand Plague and desertification from destroying the world.

( Some deconstruction, but very little is spoiled. )

Overall: A gem of a DS rpg that I would generally recommend, especially if you like games with a more serious tone and want to see time travel that doesn't rely on "San Dimas Time".