Is there any way to maintain a visa in Japan without working (or at least working 2-3 days a week) other than a working holiday?

Hello, I want to acquire Japanese citizenship.

I need to live in Japan for 5 years, and the only visas I can get to live in Japan with are Working Holiday and Employment Visa.

But the problem is that if I live in Japan with a employment Visa, I have to work 5 days a week, so I don't have enough time to study on my own.

(I only want to work 2-3 days a week. I have to study at least 8 hours a day 🙁 )

Can you recommend a way to maintain my visa while living in Japan like Working Holiday without having to work? I asked GPT about this, but none of them applied to me. (For example, family in Japan, research purposes, cultural experiences, etc.)