Fates and Awakening based the ending certain characters got based on their S rank. However, in 3h the highest you can get is A(a+) so instead it's based on who fight next to each other more often. Meaning if you wanna "hook up" some of them you gotta base your tactics around that...
Ooh wee. It was more simple back then. Though I like the idea of it now being based on realism. The more you fight with each other the more you bond too. It’s like a shonen manga lol.