Not sure about the popularity among tcc'ers , but I'll try this year.
As far as I researched, there are two more Mt. Fuji related hill climb races.
1.Fujisan kokusai hill climb race(a.k.a. Fuji Azami race) ; June 19
Average Grade 10%
Maximum Grade 22%
2.Omote Fuji hill climb race ; April 24
Average Grade 6.9%
A bunch of us on here did this "Fun Ride" race last year and some did the other far steeper and shorter Azami race that was on the same day. I did the "Fun Ride" and enjoyed it. Even got a bronze spacer in the mail a few weeks after wards to signify that I finished with in 90 minutes. Gold for sub 75 mins?? It is 24km up to the 5th station on a road that is normally full of traffic. We rode out there the day before and stayed the night near Kawaguchiko. Might try the Azami line race this year instead.
I'm leaning towards the 'fun ride' again. Its more hill for the yen, if you ask me. However the hardcore Krewe will generally try the Azami climb - which is, unfortunately, the same day! Go figure. Hopefully can do this again with Keren, Kim and crew - it was really a great time.