I never get that dialogue choice even though i dont skip through text at all. She just says that Aya is too slow, and just bails
Walkthrough included with game completely skips on that part, and it seems no one gave actual proper answer to this.
You need to be
Best friends with Aya to get good ending. There are two points in game where you bond with Aya.
First I don't remember and I think it may be automatic. It certainly happens before you start chasing Mika around. After that event game will say Fuu and Aya are now Friends.
Second I believe unlocks once Fuu finishes business with gangbang group. She takes camera from them, and it appears in Item Menu. To make this bonding event happen, you need to get to Aya's home, and interact with toilet room right of Mika's room (it will have "interactible" sparkle effect).
After it, game will inform that Fuu and Aya became best friends, certain dialogue in first encounter with Akame before chase will change, and after it, when Fuu unlocks her powers and prepares for decisive attack, there will be a choice to wait for Aya or to consider her too slow.
I gotta sleep so I can't check, but I think "Chase" gameover animation scene is also tied to this, because without best friends stuff, all I got was "Fuu erases Aya's memory near shrine and game quietly shows GameOver screen".
Edit: Yes, "Chase" scene also requires to be besties with Aya.
Finally, there's only one "Extra" scene, with swimming club. Scene text to "Shut-in" you need to unlock in-game, by talking with him when he's working. Probably after shoplifter scenes, but it works if you did everything save for final fight with Akame.