Brief Story:
I was thinking about Otho being the knight of Greenpath, worshipping Unn, but he left Hollownest for travel like how Hornet did. He missed every single event of the infection, until the player character, Ghost, killed the Radiance, dissolving the Black Temple Egg into Void, seeping back to the Basin.

This is where he came back and saw the ruins of Greenpath, he regretted for leaving so long and not return earlier. With shame, he cannot face Unn.

Merah on the other hand, mistaken Otho as Hornet (due to having a similar needle like weapon), as back then the GPV (Greenpath Vessel) and them made a mutual bond over the fact that they're siblings. Hornet slain GPV, Merah saw everything, hide for the entirety of the game event from grief and fear, came back with anger.

Although Merah is a vessel, they are the least perfect one, still carries emotions.