What should I do with a mouldy futon?

Okay, so I've been living in Japan for around two years now, and I have just noticed that my futons I bought when I first arrived have an incredible amount of mould on them. Now before you judge me, in my defense I was completely unaware that you have to fold up your futon every morning after sleeping and put it outside weekly to air it out - I've only just started doing this now. Is there anyway that I can get the mould off my futons, or should I just buy new ones? Or are there any cleaning services that might focus specifically on getting nasties like mould and mildew off of futons? Advice and not judgement on my misinformed brain would be much appreciated. Ty.

Buying new would be simplier.

Not just simpler - safer too. Safer for your lungs. But that said, the direct sun does a good job of killing mould and mildew. Unfortunately, the season isn't right for a bake off. If it were me, I'd buy new.

Also - I'd go over all surfaces in the room with bleach.

I would also buy new. Futon are something you use for 6-8 hours (or however long you sleep) every day of your life. That is not a point to be frugal on! You don't want to risk breathing in the mold all the time, or never being sure you've killed it all. Start over fresh.

Next, what kind of surface are you putting the futon on? Tatami or hard wood floors? Depending on that answer, there is slightly different care for the futon AND the floor. However, regardless I recommend putting wooden slates underneath the futon to help air out under it, especially if you are not the tidy type who will fold and unfold every day (like me!). The slates underneath my futon meant I only needed to put them out about once a week to once every two weeks, as they didn't get moldy since there was airflow underneath them. I would also directly vacuum them when I brought them back inside. They make special futon vacuums that are said to help clean and get rid of any dani, but I just used my regular vacuum cleaner. You can buy those slates in different styles at any home improvement store, such as Cainz Homes, Nitori, Sekichuu, Viva Homes, etc. etc. You can buy the special vacuum at those places too, if that's something you're interested in.