That was cute.
That said, I don't see it being sustainable as a full blown series. There's only one joke here, and it would get old pretty quickly.
I could see this being done in 3 volumes, maybe 4. That's only if it's just the two of them, though, unless they decide to add more assassins/love interests to up the stakes. Since there were other relatives in the main guy's family who are out for his inheritance, the potential for competition of who would get to him first (killing, love, or otherwise) can really stretch the series here like that other story about the OP hero's party members trying to assassinate him.
Heck, each of the love interests could have their own gimmick in their method of assassination (poisoning, sniping, trapping, straight-up violence, the list could go on).