So, can someone explain the Forunner story?

With the didact, librarian, all that stuff. I’m planning to buy the books, but I’m still fairly confused. Who are they? Why is the didact on requiem?

The Didact and Librarian (She is dead, we only meet a fragment in the game) are/were a couple. The librarian indexed all life forms in the gallaxy while the Didact fought the flood before they fired the halo rings. Incidently the Didact dislikes Humanity because at one point umanity rivaled the Forerunners tech wise and some said they should have been entrusted with the Mantel. humanity encountered the flood about 125k years ago were fleeing from it and ended up fighting the Didact on one side and the flood on the other. Didact defeats the humans after 25kyears and devolves the entire species. They then discover humanity found away to defeat the flood but it was lost when they devolved humanity

requim was a forunner planet

humans were attacking forunner planets

after many battle the diadact reacted and stupified them, made them simple cave men basically, the librarien didn’t like this

the librarien and diadact are married

turns out they were destroying flood infected planets not power hungry as thought before

diadact (kinda the military leader) uses the composer to turn his willing soldiers into prometheans, didn’t have enough so he takes a load of humans to make more nights

librarien wounds the diadact and locks him away in requim (in that red/black ball) and tells him to meditate on the matter

halo rings are fired

skip forward 3 million years

diadact released by MC

side note

forerunner “religion” as such is “the mantle” in which they have to protect life and use it to uphold their morals and such hence why they attacked humans so much

the diadact believes that “the mantle” is the forerunners alone to hold, the librarien says that the humans were kinda doing it as well by wiping out the flood and the diadact doesn’t agree and is angry, this is why she tells him to meditate which of course just made him angry