Imma spoiler tag this, it's how you get the different endings BUT there are also many other huge spoilers:
Spoiler Below When Altessa the dwarf gets ill after Mithos attacks him and you find out that Kratos is Lloyd's dad, you have to go to Flanoir, correct? Well, in Flanoir four people leave the city, and Lloyd and the other three stay.
Now, depending on what choices you've made throughout the game, what you've said in those light ring skit things, and other stuff, some characters will have a higher affection for you.
The three characters with the highest affection for you will stay in Flanoir. The person who likes you most will knock on your door at night. If you refuse them, the person with the next highest affection level will come. If you refuse them, the third person will come, and if you refuse THEM Kratos is the default. If Kratos is one of the three people who likes you most then Colette is the default.
So, whoever you agree to go on a walk with will be the person your ending is based on. Here is how the ending will differ:
-Right before you go into Heimdall's forest to fight Kratos and release Origin's seal, the person will go on another walk n talk with you.
-After you fight Origin and Mithos comes alive in his Cruxis Crystal, he will possess and kidnap the body of the person you spoke to in Flanoir. If Kratos is the person you chose, then Colette gets possessed.
-If you do Kratos's ending, Kratos re-joins you after the Tower of Salvation thing instead of Zelos. Also, you kill Zelos.
-At Dirk's house near the game's end but BEFORE Flanoir (I think...), all the characters will be spread out for you to talk to. The character with the highest affection will be on the terrace, and you must speak to that person to proceed.
These last two aren't considered spoilers so:
-Throughout the game you will notice several other things differ depending on affection, even before the Flanoir scene. For example, a 'Combo!' skit will appear with Lloyd and whoever likes you most every now and then.
-To know how the characters feel about you, talk to the Triet fortune teller. She'll tell you how each individual character feels about you, and if you say 'I dunno', she'll describe the person who likes you most.
Also, due to these extra scenes and stuff with the highest affection character, doing a certain character's ending will tell you a lot more about that character. In Zelos's case, his past is ABSOLUTELY shrouded in mystery unless you do his story, and his story is just OMFG SPOILERS DEEP STORY JUST WOW. Or so I've heard. I'll let you know when I actually get to his ending. I still have three more before that. :P
This could be considered a spoiler, but it's not like OMG SPOILERZ bad:
Spoiler Below Oh, and the really funny thing is that you can kind of alter Lloyd's love life depending on who you choose. If you pick any of the girls, then Lloyd and the lady you choose will develop feelings for one another. Yes, this includes Raine. Trust me, I just did her ending. XDD