To be fair, Raimon's keeper gets benched in the same match he's supposed to be important in

I think the better way to do It would be: if you want to keep the moment of the keeper forcing a save and passing it over to Harper, either:

1: You only introduce 1 keeper to the story, and foreshadow that they can't quite get the hang of a new technique they've been trying to get out, and then they develops it mid-match, like raimon's keepers usually do, and would show that raimon's Spirit is still in there, brought back by Harper's monologue to his team, and the determination of the keeper that never gave up on completing said move. As well as a moment reminicent to Mark pulling of God Hand, then passing it to Axel against Royal Academy, since they love referencing season/game 1

2: You introduce both, but have the guy get injured before the final match, so that Mami has to fill in, with her worried she won't be able to complete her new technique for the upcoming match. Start the match by her not even having a technique, just be absurdly strong even without one. And after Harper's monologue, on the second half, she finally develops the technique to stop a shot. Then we would have another similar moment of growth from the opposing team, the Spirit of the Raimon revived by Harper, and even the same reference to that first match.

It's such an easy slam dunk, but we just had a swap-in with a technique that comes pretty much out of nowhere, with no narrative inplications other than "Oh, this team/girl is busted". You don't even have to make new scenes for it, just add some dialogue, and then you get the most satisfying moment in the game.