Wow - I hope it doesn't require a lot of work for so little reward! But, it's quite beautiful and you got a wonderful photo of it to share with us. Thanks!! (Happy to see you posting again, my friend Masaki!)
20 years is a long time to have a plant. You must take great care of it. Very lovely flowers! I have had a Hoya now for about 12 years. When I changed it's location it started to bloom. Now it has flowers quite often through the year.