My theory is that Marino's parents were really angels sent down to watch over the neighborhood. That explains why they have so much money, God just gave it to them to live comfortably! Takatsuki and Yuu are angels with a lower rank. They have served Marino's family for over a millenium. Marino's parents had to marry her off to an angel with an equal or higher rank to guarantee the family's property and bloodline would continue. This is what Yuu's dad reminds him of right before he goes to dump Marino. "Her family will always be greater than ours!" Or something similar. Marino hasn't remembered that she's an angel because not all of her memories came back, and Yuu is just embarrassed about it. He doesn't want the guys in the dorm to call him Angel Face or something like that.
Marino's parents being angels also explains how they managed to get to the beach at almost the exact same time as Marino, even though they left later. Supposedly, they couldn't have been on the same train or even on ones with close to the same arrival time or else they would have bumped into each other in such a small place. So, therefore, her parents flew to the place. Marino couldn't fly yet because her wings haven't fully formed and she hadn't developed the power to fly.
Now, for the truck. The truck was driven by a demon. In the demon world, when you kill an angel, you gain their power. Just like leveling up in a video game. There was one fairly high ranking demon who took it upon himself to kill the little family. He was hoping to kill Marino along with her parents, but he had a problem with his depth perception. He thought Marino was closer to her parents. Anyway, parents are dead. There is such a big crowd, he decides to finish off the little girl later. He puts a track on her mind, thinking he could just kill her in her sleep in the next few days. Whenever Marino faints and loses her memories, the track is lost. She goes to live with her aunt, who was such a shame to her family because of her lack of angel abilities, she was disowned. This is why the demon didn't know where Marino was. The aunt tries to restore her honor by trying to marry Marino off to high-ranking angels again. This is when Marino runs away. Satoru/Sei/whatever and his brother are both angels trying to prosper in the human world. They are in a lower class than Marino; that is why their dad wants them to marry her. He wants to raise their rank in Heaven.
When Marino regains her memories, the track is reinstated and the demon is notified. He, by now, is much more powerful. He can't infiltrate the boys dorm because Kaoru comes from a family of renowned exorcists. Most of the demons he has exorcised have been females, thus his fear of women. The demon waits until Marino is by herself before he can fulfill his plans. He sees her in the train station, but there are too many people around as witnesses. Even though he is a powerful demon, he hasn't mastered invisibility. He had his chance when Marino is on the train by herself. Unfortunately, the demon is a very beautiful bishounen and he was held up by many people, and missed the train.
Finally, he just uses his old truck to try and rundown Marino like he did her parents. When Yuu saved Marino and kissed her, both of their powers rise to impossible heights and the demon blows up with the truck. After their powers are elevated, Yuu passes out because it's more than he can take. He becomes a much higher ranked angel, so now he can marry Marino without regrets.
Chihaya is an angel too.. that's why he always knew where to find Marino! (I liked Chihaya the best.)
The end.
Okay, seriously guys, this manga... it was pretty terrible.
So, what do you think would have made it more interesting? I think if the plot development would have been better and the leading heroine wasn't so typical, it would have been better.
