Is risotto or paella rice a better substitute for my Japanese dish?
There is a QA about the differences between paella and risotto rice on this very site, but it doesn't really answer your question. 

For your purposes any arborio rice will do, the secret is to make it sticky using technique. Firstly, don't rinse the rice, you want to keep the starch, not wash it off. Next this you want to first put the rice and water into a pot and let it sit for a couple of hours, this will loosen up the starch on the outside of the rice. Then cook the rice as normal in the same water you soaked it in, letting it sit for 10 minutes after it is done. Don't stir, you want to keep the starch on the outside of the grain as much as you can.