Since Ritual Blood (4) is such a high grade material, a lot of players will take issue with how long it will take to even create the Ailing Loran Labyrinth. As such, the fastest, safest way to acquire this material is to farm the two Kidnappers in the Layer 2 of the Lower Pthumerian Labyrinth.
Progress through the Layer normally, but then go to the optional area before the boss, in the final hallway. This will eventually take players to a spiked gate that opens to the side of the path near the lamp so that backtracking will be easier.
Once this is done, simply go from the Lamp, down the first ladder, take a left to the large room with a chest and a Labyrinth Watcher, and climb the stairs. Instead of dropping down, circle around to the room on the same floor, and there will be two Kidnappers, one near the staircase, the other atop of them. Kill them and reload the area to keep farming them.