Studying abroad in Japan for a year, what to do with my phone plan?

I’ll be studying abroad in Japan for a year soon, and I’ve been trying to figure out what I’m meant to do with phone plans, wifi/data, etc.
I’ve tried googling this, but I can never seem to get a straight answer, or the answer is too confusing. Using an international plan for my current provider is too expensive for a year, I’ve heard mention of ‘SoftBank’ in Japan but without getting good explanations for how it works, suggestions of getting a new SIM card or eSIM card but I barely understand what those do, or just straight up getting a new phone for while in Japan.
I don’t need to be able to use iMessage or make calls using the built in phone app, because I’ll be using apps like LINE and WhatsApp to keep in contact with people anyway. Mostly, I just need a way of accessing the internet wherever I go, either via data or some kind of mobile wifi device.
I was hoping someone could help me, give me some options or just straight up tell me the best method. If so, please use words and explanations that you’d use for a 5 year old, because I just want as simple an answer as possible.
Thanks!