That's not the interesting part. The interesting part is seeing the fallout. When Marco was told of the power of the Blood Moon, she either didn't understand it, or didn't believe it. Marco, on the other hand, when he had it ominously whispered to him, immediately bolted for the Underworld so Star wouldn't be bound to Tom, attempting to get her out of Hell, only to find himself under the light with her. So far, the Blood Moon phenomenon is something only Marco has recognized, and only in moments where he would feel guilty about "betraying" her, such as when he kissed Jackie.
The end result, as I see it, is that Marco feels obligated to be with Star because fate dictates it, and Star has shown time and again she hates constraints like "fate" and "destiny" (becoming a queen, or fucking DYING). Add on to that Star's question of if Marco likes looking out for her because he likes her, or because he feels obligated to, and you're going to find some interesting conflict.