Edit: does that six pointed star have some special meaning in japan? I know michiru also uses it. I assumed that mel was some kind of halfu jewish-japanese initially, same with aki rosenthal - but have since assumed its just the japanese not having to deal a lot with the tribe and thinking its just a kind of novelty than something of significance.
Edit2: I just realized the star has been historically used with vampire characters, because you know, Jewish people stealing the blood of christian babies to sacrifice to their demon gods etc. or something. With Mel being a vampire that would make sense if thats how the artist came about the idea of using the symbol for her.
It's a fairly basic symbol - just two overlapping triangles - so multiple cultures throughout the world have used it. Besides Judaism you can also find the six pointed star in Shinto, Buddhist, and Hindu symbolism. In Japan apparently it is known as the Kagome pattern and is thought to ward off evil, but I'm just going off of Japanese wikipedia lol. It's not super popular in Japan, so a fair amount of modern Japanese media that use it may also be referencing the Jewish Star of David, especially chuuni media that leans into kabbalah symbolism.