It's more like 80 ending 'segments', where the characters will have different final interactions depending on their relationship levels with each other.
The easiest way to get different endings is by making characters read the books written by other characters. Each has two types, one that raises friendship and one that raises love. Depending on the rating, you get different endings. Doing things like reverse side lowers ratings, as well as pickpocketing with people in your party, etc.
Look at the FAQs for more details, but that is the gist. It's a little hard to predict how things will go, though. The endings all resemble PA sequences, they aren't animated or anything. Also, its not possible to have same gender love, lolwot.
Get Leon to have love rating with anyone and it is lol.
Spoiler: Star Ocean: The Second Story FAQ/Walkthrough Final - A I e x
--------------o Secret Endings --------------o
This was taken from EternalSphere's topic, originally posted by Wallwalker/PWOPLW. Give credit where credit is due.
There are three endings that you can only get by doing certain things. Two of them are only available in Rena's scenario.
It's possible to get a character who's unlocked one of these endings with another character if their emotional levels for someone else is as high as they can get. But that's difficult to do.
Opera: Go through the game without getting Ernest.
Ashton: Only available in Rena's game. If you do a PA in Herlie after you get Ashton and before you start the Tournament of Arms, he'll meet the sick girl and talk to her for a while. Do another PA, and you'll learn about something called Metox. It's in the Lassguss Mountains. (There's a side trail that you can take that splits off from the main path and curves to the left. It leads to a desert area. The Metox is growing along that path, so keep an eye open.) Head back to Herlie, save, and do another PA. If the girl survives, Ashton will get a special ending. (Note that you can also help the girl in Claude's game if Bowman is in the group, but that doesn't result in any special endings.)
Celine: Also only available in Rena's game. Do a PA in Cross Castle, anytime between going to Cross Cave and visiting Lacour for the first time. Meet Celine near the diner and agree to have some tea with her. When you go in you'll see a nervous man who doesn't have any money, so agree to pick up his tab. After leaving, go back in and do another PA, and go to the restaurant again; you'll see the stranger talking to Celine, and when everyone gathers at the town gate to leave, Celine will be all flustered. Do one more PA, and head to the right side of town (down the passage near the church.) You'll see Celine talking to Chris, then you'll find out who he really is. When Chris is dragged away, you can choose to convince Celine to go after him or tell her to do as she wants. To get the ending, convince Celine to go after him, and that will do it. (You can also meet Chris in Claude's game, but only if you don't have Celine in the party. You'll meet him by doing a PA in Hilton before finishing the Sanctuary of Linga. No special endings come of it, but you can get an item from him if you drink with him.
Super Secret Ending:
All characters must have a friendship level of 10 or higher with EVERY other character, and you must have a party of 8. I've never seen it myself. There should be a video...