My one complaint is that the game still forces you to pause the action to use your magic, after you tap a shoulder button that brings the game scene down from the top screen to the sepia-toned touch screen. The transition interrupts the enjoyable experience of just running around the world (with flowers sprouting in your wake), and can take you out of the moment, albeit in a rather gentle way.
Gameplay in the Gamescom demo is based around puzzles that use both Chibiterasu and young partner Kuni, who usually rides on his back. The pair can split up with a tap of a button, and are forced to do just that to cross various bridges that are too weak or narrow to be passable together. Chibiterasu is still fully controllable with the d-pad during these splits, but Kuni has to be guided by a magical path drawn by the stylus.
This split is put to good use during a boss battle at the end of the demo, fought against a giant fish that has swallowed some magical seeds that are essential to the health of Kuni's village (of course). Once Chibiterasu has forced the seeds out of the fish's mouth (using a combination of standard attacks and magical slashing), the player has to guide Kuni with the stylus while also protecting him from the fish's disturbingly long, waggling tongue.
It's hard to judge just how well this partner-centric fighting and puzzle-solving will develop from what is essentially a tutorial level, but as a proof of concept Okamiden's Gamescom demo definitely proved that cute, magic-infused Japanese landcape paintings can work on the DS.