boktai has a special sensor to acquire light from the environment and that helps power some of the in-game tools. since emulators don't have a way to measure light, it's hard to emulate it
I've also used the patch to play the Boktai games. The first game always worked fine for me, however, it's sequel "Solar Boy Django" had a bug in the patch where every time you entered a room, the sun guage would go to zero again. This made some things, like solar forging, almost impossible.