If you take a tekked Paku Branch into TTF, beat the dragon, and go to the med center, you can warp down to Ruins 1 and stand beneath the waterfall for a period of time. If you do, it will convert to a Striker of Chao; this method is a lot nicer than than the other, which is to create a chao mag entirely and then throw it on the paku branch.
heres a video-