Rapini (broccoli rabe) is called nanohana in Japan. Actually, nanohana and rapini are not exactly the same, but close enough to substitute. Nanohana is softer than rapini, but rapini is sweeter than nanohana.
The mixture made of freshly ground sesame seeds, sugar, and soy sauce is called goma-ae (sesame mix). We mix nanohana in spring, and spinach throughout the year except winter. This is a side dish, but I love to eat it on rice.
The only caution is not to boil greens too long, as you don’t want to lose the fresh texture and bite. The greens are moved to ice cold water right after finish boiling, in order to stop the cooking process immediately. Make sure that ice cold water is ready before start boiling the greens.