>>40977507Ralts should be the first town, when you're learning the mechanics and first getting her. Establish why the character is responsible for her and why he feels that way.
Kirlia evolution could be the bookend of this sequence. It could be the part where the main character's feelings of responsibility to her are first reciprocated, and you first get to get to know her as a character. You could also foreshadow problems that could come later ("It's fine to have a pet but if you're going to he one of -those- Gardevoir owners there's going to be trouble.") This would probably be the sequence where you teach the main mechanics.
Gardevoir evolution should be a really emotional moment but also fairly early, since it's going to be the meat of the plot. This could be the part where they start travelling and going to different towns, which would be a change from the safe domesticity of the first segments.
I don't really know what story you want to tell though so those are just some ideas.
>Where would the tension come from?He could get kicked out of his town or run away and they could try to find a better life for themselves. Or she could have some kind of mission she needs to fulfill and he leaves his old life behind to help her. Either way, something is lost for a whirlwind chance at happiness that could be a huge mistake.