Sai Cafe in Himeji is an amazing vegan restaurant with a menu that is supervised by the head chef of the popular Saido restaurant in Tokyo. Although this cafe may not be the easiest to get to, it is well-worth a little detour as the food quality is top-notch. You can find beautifully-presented dishes including ramen, katsu curry rice, tempura rice bowl and more. English menu is available, but it's not as updated as the Japanese menu, so I'd recommend translating from the Japanese menu to see all the dishes.
The atmosphere is calm and relaxing, and the staff is friendly. The closest train station is Nozato, which is about a 20-minute walk away.
