Internet in older building

I'm not super tech savvy, so apologies in advance if this seems simple or easily googleable (I tried but couldn't find the answers I was looking for). I just moved into an older apartment building that said it offered free internet. My previous apartments all had LAN ports in the wall but this place only seems to have a phone line (labeled MJ-4W) that would need to connect to a modem in order for me to actually connect my router.

I've lived in Japan for a few years now but because I've never needed to set up internet I'm not really sure how this process works. Assuming the apartment already comes with internet that's all done through VDSL connection, who would I need to contact to purchase or rent a modem?

I've also done a bit of research into getting a hikari line installed but I'd need to talk to the building manager about that. I just need something so that I'm not eating up all my data for the time being.