It’s a visual novel so it will repeat all the information you need. Outside of that.
Realize that for the world they knew Kurisu for a short period of time but Ryouma knew her for what might have been years. He’s in fact had years of experiences with everyone.
Also the Suzuka you meet in Zero is not the same person as the one from S;G. She’s had a completely different lived experience.
Will say been thinking about this game recently as
The mid-section of the game where he keeps going back to prevent Mayuri’s death as a meditation and realization of how someone deals with death and keeps replaying in their head how we could have prevented it. Of course he does eventually prevent it in the shittest story way possible.
The Luka section is still horrible. They did not get better about that.