Urgent Moving Help/Advice (moving company fell through)

Hello 🙂

I hope everyone here is having a good day : )

My visa to Japan ends next week. I had a moving plan all sorted , but it has fallen through as the moving company cancelled it ( I don't really know why , they just contacted by email). I need to leave the country in 6 days and have lots of stuff I don’t know what to do with , and don't want to just throw or give away.

My accquentences have not been helpful as they just told me to dispose of everything apart from a few clothes and a couple of books (ie, get rid of all my other cloths, personal affects , precious books etc) I don't want to do this.

I have 15 boxes (5 100size and 10 160size) and 4 pieces of furniture. I was going to take the furniture with me ( quite nice handmade wooden table that can become kotatsu , really nice zabuton and so on ) as they are things I could not get in my home country, but if needs be I will leave this with friends and give away.

Therefore, I would only need to send the boxes.

I thought about sending through ゆうちょ slow ground mail, but am not sure if it is possible.

5 of these boxes are just random documents, notebooks etc for work. Since I was told I have to itemise the whole box, do I really need to write an itinerary for each single loose page, or each book ? There must be several hundred single sheets of paper in there too, from letters and cards from family to personal notes and the like. There are a few pens, pencil sharpeners and a lot other random stationary chucked in too. How do I even fill out a customs declaration for this ? They asked for the price of each item, and to have each item's "HIS" code ( I think its called this?) but I have no idea what that would be. A lot of it is work archives, personal notes that I sometimes need and refer back to etc, so I don't want to just destroy it all. There are a few reference books chucked in there as well but I don't remember which box. ( They are already packed and sealed)

Another several boxes are full of books (46 books in total). Is it possible to send these things? I heard there is a printed matter option but the local post office said it was only for packages with say one or two books in, or a single magazine ( ie. if you fill a few boxes with books and magazines and have many of them you cannot use this service.). It also does not apply to written loose leaf notes according to what they said.

The rest are just clothes, and random personal artefacts and house… things(?) ( think vases, house decerations , cups etc) All personal things that were either gifts or something meaningful for me. I do not want to dispose of them. They are mostly very delicate.

These more problematic articles make up a few boxes, with the rest of the boxes being clothes (big jackets and so on , which I can easily deal with and do customs for)

Any help on the options I have , or advice on whether I should proceed with ゆうちょ is very appreciated. Thanks for your help in advance!