It has build in list of free public vpn ip's. Some of them are Japanese. (The speed is horrible though)
You can also use custom ones using this software.
Can be a bit tricky to setup the first time but nothing crazy.
I finally 'bit the bullet' and got a Planet VPN paid membership.
10 dollars a month and I only check for the 'good stuff' only about every six months on DLSite so it was worth it for 20 dollars a year.
I don't know about paid options, but have you tried https://www.vpngate.net which are free? They may be slower, but worked when other free VPNs set to Japan couldn't on certain sites.