I'm fairly new to the community and might get some stuff wrong, but I'll take a shot at answering this. The game is currently in the "harem route" which we have recently learned is the first five chapters. After that will be the "dark route", which we don't know much about, but this is a game about being happy so I can't imagine anything will go wrong. Remember to smile! Then there are the "purity routes", which from what I understand will be "good ends" for all of the 35 girls. Finally there is a "true end", which again we don't know much about, but probably involves leaving the "simulation" or whatever the fuck Kumon-mi is. So it's probably unlikely that there is any sort of harem ending at all.
This is very possible. There is an event ("First Contact"?) which describes a car crash, ending with the line "Why did it have to be him?". It's been theorized that that is Nozomu asking Sekai about Akira.