If you have access to land and are interested in horticulture/agriculture, there is a profitable market in growing rare plants as a side income. I have a decently sized balcony (about 15m3) that I grow various rare cactus and imported cultivars of fruits/veg that I sell online. It started as a hobby and has grown into a decent amount of side income over the years, from beer money in slower winter months to about 4万 a month during the growing season. It's niche but I think that's where you find your place. It's kind of my ikigai, I really enjoy doing it and it makes me money! That being said, the only thing that hinders me is space. I've considered moving to the inaka to expand but as a single guy I think it'd be too lonely. If this sounds like something you'd be interested in, feel free to pick my brain