Both of these manga revolve around a guy who has a special, supernatural, heart. In both cases, these supernatural hearts attract powerful superhuman and inhuman foes, as well as some powerful allies. The guys must fend off those who want their hearts, or their very lives will be forfeit.
The story of both of those series goes like this: A wimpy guy has a special heart and a harem. Nither of those manga is particularly good, but if you were fine with one of them, then you'll probably be fine with the other one as well.
The main character of each of these series has a special heart that everyone wants to take possesion of, to gain it's immense power for themselves. The main character in each series has someone with great powers trying to help them & ward off everyone else.