In short, yes, there are channels you can subscribe to monthly for unlimited views. Not sure if there's a R18's "prime channel" equivalence.
I don't use R18, mainly use DMM for gravure idols stuffs.
A little update for interested parties.
I bought a gift card from another site(before I saw fletcheree post) and redeemed points with no issue.
It seem buying from amazon is the best option since there's virtually no price markup(other than currency conversions and card charges).
Other possible...
I did not notice this. No wonder my VISA debit card no longer works on DMM. Thought I wasn't affected by the Mastercard situation.
I guess DMM gift cards is the next viable option.
A lookalike AV gal I stumble upon. Might interest you....
https://www.akiba-online.com/threads/rebd-594-noeru-honda-noeru-noeru-jump-out-and-fairyland.2050458/