The problem here is that it would start off in a way that people who start to read it will think "Oh dear, it's another of these generic ones" even though you have a twist. And the only way to convince them otherwise is to spoil the plot which then sort of defeats the point in them reading any further unless they have a curiosity of how exactly it goes wrong. The only way, that I know of, really around this is to start with the end to make people curious. It's a difficult situation that I've been in myself and I never managed to get out of it.
I've been told and as people have then told you, the key to doing a trainer fic right as it were is to make it different. I think one thing that hasn't been mentioned is that it should be obvious that it's different pretty early on so we don't get the "here we go again" thoughts I mentioned earlier. You said that your trainer is a minor character of the game plot, well, maybe you could use that to your advantage to deceive your readers into thinking that it's not a trainer fic, or at least that your trainer isn't the main character that we're familiar with. This might not be possible though because I obviously don't know which minor character you're using.
Hope that helps.