In 9.1.5 they buffed the mobs inside the Rift in Korthia; they now drop
Fragment de reliques too! However most of them have quite a poor drop rate except for the big elites called
Ténèbres faméliques. These have a similar loot table to rares in Korthia; the only difference is that they are much easier to farm, since there are a lot of them.
Their numbers are especially large in the Maw, which most people might not think about. You are also able to skip the root NPCs completely!
Depending on your Archivist's tier, they will drop a different number of relics, however at Tier 5 you quite often see 3 to 4
Cube-rune déroutants or
Motifs fäe déchirés, granting 150 research each.
Also keep in mind you need to be Tier 4 to be able to keep buying the
Clé de faille réparées, but reaching Tier 4 goes quite fast these days. Also the rares in Korthia have quite a solid key drop rate.
By forming a party of 5, I was able to grind about 9250 reputation in 1 hour and 5 minutes. By maximizing the route and RNG, you can definitely reach 10k reputation an hour without too much trouble.
The most important thing is that you grind it early, before more people figure it out and start to farm the Darkness!