Otonashi died before Kanade how did she came to afterlife school before him?
remember Otonashi decided to donate all of his body parts momments before dieding in a train accident and yet Kanade reaches the afterlife school before him am i missing some backstory about Otonashi arriving late to the afterlife school
Remember, Otonashi died with his heart's desire. He passed away and living up to a happy life (due to the fact he donated his body to people who may use it of value).
The Afterlife School is built for young soul's who were not contented in their life or you could say people who could not meet their dreams in life (so Otonashi isn't really fit or have no connection about that world). This is when Kanade comes up- Kanade wanted to "thank" the person who saved her (the one that donated a heart,Otonashi). But since Otonashi died long before- Kanade couldn't "thank" the person, that's why she ended up in the School (not having her life fulfilled). In Otonashi's part, since he is needed for Kanade's wish to be granted- he was revived at the school for that mission. And because of the span of time til he got back to life again, somewhere he had lost his memories causing amnesia.
Overall to sum it all, Otonashi was needed for Kanade's wish- the reason why he was summoned in that world. Even though he died first.
Otonashi died before Kanade is right but he donated all of his organs so that made him not able to go to the afterlife world yet because the people who got his organ died after KAnde's wish to thank Otonashi. so technically Otonashi was still alive but in different bodies thus after all those people dies making him go to the afterlife world to fulfill his life goal which is to grant KAnade's wish.