Glad to hear they’re still doing well. I stayed for a week in 2014 and went there 3 times, including on consecutive days. Took my parents, who live there but don’t often trek into Waikiki, and they’ve been back on their own since.
There’s a similar place in Ala Moana (Iyo Udon), but I like Marukame better. Marukame feels more Japanesey and Iyo feels more local.
My wife and I were just in Waikiki a couple weeks ago on vacation. Sounds like I missed out on some good eats! (On the other hand, it’s doubtful I could have got my wife to go to a Japanese noodle place anyway. )
There’s a downtown branch too, on the corner of Hotel Street and Fort Street Mall. I’ve not tried that one yet, but it’s reportedly popular too. It looks crowded at lunchtime when I pass it by.