I know a lot of people haven't seen Sailor Moon Stars since it didn't come out in the United States so I'll give you a little brief on the situation of these two guys for those who don't know.
*****Warning - If you don't want me to spoil some of the story then don't read this.*****
Okay, in Sailor Moon Stars, in the first episode, Darien leaves to go to school in the United States. Serena and Darien promise to write to each other.
Enters Seiya... a man in normal day and a girl when he/she transform into his/her Sailor outfit... (weird, but forget about him being a girl for your answers). The first thing he calls Serena when he meets her is the same thing Darien calls her...(meatball head in the english version, dumplings in japaness version). It turns out that he will be going to the same high school as her...(Yes, she got into high school)
As the story goes on, Serena writes to Darien everyday but receives no reply...(because Darien was killed on the way to US). So, after being around Seiya for a while, the two of them seem to hit it off. Serena, of couse, loves Darien but begins to lose faith in him since he doesn't reply back to her.
Meanwhile, Seiya has completely fallen for Serena by the middle of the season. He is even about to tell her the truth about his other life, but things keep on interupting his attempts. He's willing to do so much for her. Serena has also developed feelings for Seiya by this time.......soooo.......who should she get with eventhough the story has already been written. I'll give my answer and reasons later......