A good deal of the Bakemono in the story are given quite sad backstories.
The death of Hizaki Mikado.
Minoru's "father". And Ushio's delayed breakdown over it later with Asako.
The part where either Asako or Mayuko must sacrifice herself to make a new Beast Spear that has everyone crying, even the bakemono who don't really want to do it either but have no other recourse. The whole arc becomes one long tearfest as important characters one by one vaguely recall someone who touched them Ushio and Tora but because of an enemy's attack, can't remember exactly who and why.
Nagare's backstory and reason for his Face–Heel Turn, as well as how they are revealed. The Hakumen no Mono enjoys causing this sort of thing.
In episode 9, Juurou's vengeance against humans due to being forced to constantly move away from humans developing land around where they lived. Ushio then relates to him by giving him a story of he too losing a jungle gym he loved and watching it being torn down due to safety, and being helpless to stop it. Though Juurou stops killing people, he ends up killing himself when he attacks Ushio, prompting the Beast Spear to stab him. He then tells his brother and sister to live on, and that his death was for the best.
Hyou's death after finally avenging his family against Guren. Even worse after the "He just went home." line.
Tora: "There's a hole... in my chest..."
Tora's backstory, which also reveals the origins of Hakumen no Mono.
Tora sacrifices his life to defeat Hakumen no Mono, yet Ushio begs him not to go as he hadn't eaten him like he had said. The smile Tora gives and Ushio's gut-wrenching cry as he disappears is hard to take in all at once.
