Saragimaru's backstory is tragic enough, especially when paired with their theme song. They were born from Orochi's corpse, along with seven siblings (Yaorochi included), but as centuries passes, most of them died, leaving only the two of them. Saragimaru wants to bond with their only remaining sibling, who is too obsessed with the legendary Tasouken to notice or care about them. During a fight, Yaorochi attacked them with the Tasouken, and given the sword's ability to sever relations, it ended up severing their relationship. Yaorochi left to find a way to restore the Tasouken and Saragimaru looked after them for years and even requested Sukune to make a clay sword similar to the Tasouken in order to make their sibling happy. By the end of EMS, they know that Yaorochi will never recognize or love them, but as long as they could protect them, they are happy.
In the Extra Stage of Earthen Miraculous Sword, it's implied (later confirmed in Brilliant Pagoda or Haze Castle) that Tsubakura is homesick for the Outside World. No wonder why they are so bitter with everyone, having being forced to do an occupation in a strange land.
At the end of the Brilliant Pagoda route, Mitori outright tells Kuroji that they're not the greedy self-centered bastard they claim to be. Aoji and Hooaka actually laugh at the answer, while Kuroji stares down at the sky, complete with Dull Eyes of Unhappiness.
Mitori: Kuroji Shitodo.....What do you truly desire? Kuroji: ....What are you talking about? Mitori: I can tell after our fight that you actually don't want power for personal gain. Hooaka: Eeh?! That's not possible. Aoji: Kuroji is the kind of person who lives for their personal gain, you know? Kuroji: ......
It's already sad that even Kuroji's closest friends (Aoji, Hooaka, Saragimaru) believe that Kuroji is an awful person.
Mitori and Iyozane's backstory. Despite the horrific things Mitori's done in the present, you can't help but feel for them when learning about their past, such as Mitori's mistreatment by the royal family for being a bastard child and Iyozane's fall from Riches to Rags.
Mitori: So in other words, Iyo is Our enemy now.....How sad. Iyozane: Well, it's not that bad. I'm glad to see you again.
Chouki's backstory. They were raised to be Fumikado's servant since childhood and they were very close. When they were working together on resurrecting the True Emperor (a.k.a Taira no Masakado), Chouki sacrificed their life in order to help Fumikado control and use the Saeda flute. However, it was a Senseless Sacrifice (being dead and unable to inhale/exhale air, Chouki couldn't use the flute at all) and Fumikado decided to dismiss Chouki, having sacrificed too much for their sake. Unfortunately, Chouki didn't see it that way and believed that Fumikado abandoned them, thus becoming an evil spirit determined to enact revenge on their former master.
Fumikado and Chouki do reconcile in the ending of the Haze Castle route. Even though Chouki provoked the incident in order to lure and kill Fumikado, the ending reveals that in the end Fumikado defeated them because Chouki didn't have the heart to kill Fumikado and still cares about their master.
Fumikado: Anyway, Chouki. Chouki: ? Fumikado: The next time we fight, you won't win unless you really do intend to kill me. Chouki: ! ...So YOU did notiCE.
Despite her reaction whenever her family is mentioned, Hal's description in the epilouge of A World that isn't Fantasy (backside) implies that Hoojiro is desperate to find her missing younger siblings. And that even if Hal decided not to go to Mugenri, Hoojiro will go by herself.
Hal: (...Even you should have known. I was the one going along with you. I have to go, since you'll go by yourself even if I don't. Honestly..... What a difficult person. While I thought that, I sent her off as she exited the lounge car. For some reason, you could see sadness from her back. Oh, yeah, she is one of those who lost too. Desperately, diligently, with all her might. Searching, for new clues. Thinking, of the truth at the end of the line. Wishing, for the answers to the unknowns.)