Sorry for this noob question but I don't want to miss anything and I only played anime/manga spin offs of the musou franchise so far, like One Piece or Berserk.

So I know certain battles and therefore also characters are only unlocked by choosing certain characters to walk around inside the camp and talking to certain other characters that are standing around. Since there are so many characters I don't want to switch through every single one after each battle to see if there's something new.

Are those situations only one time chances or can they be done anytime after the requirements are met? Are there any basic hints or rules for this? For example conersation x can only happen right after finishing battle y or can they happen anytime after finishing battle y?