These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Tegami Bachi
I Knew It: Vallore appeared in the VERY FIRST CHAPTER doing terrible things.
Sara prevents all mail from coming to or leaving Honey Waters under the guise of being a Reverse operation, which results in the death of a man who tries to deliver on his own. But it turns out that she and Hunt had lived in a freak show, and Hunt had a dead creature's arms sewed onto him in a desperate bid to avoid being sold. When the people of Honey Waters happened upon them, Sara made up a story about Hunt being the Man Who Could Not Become Spirit in order to protect him from them, and all the other lies were necessary to maintain the first one. It helps that Sara gets a Heel Realization, leaves the money to the citizens, and leaves town with Hunt to start anew.
There's also Emil, a blind girl who was taken in and exploited by the keepers of the Wuthering Heights inn, and also formed a bond with the Gaichuu Laphroiag, using him to devour the hearts of her employers and many other people. As much as Zazie wants to stop her, particularly because Laphroiag ate his parents' hearts, he also sympathizes with her because of their similar circumstances as orphans.
Moral Event Horizon: Lawrence, the "Man Unable to Become a Spirit" sends a Gaichuu to the Veritably Abbey to eat the hearts of its residents. WHO ARE ALSO A PART OF REVERSE.
Averted for Sunny, who is a victim of the above.
They Wasted a Perfectly Good Plot: Anime-only. Just what happened in the past that caused the real sun to go out? Where did the gaichuu come from and why do they anachronistically look like robots? Why is there an Eldritch Abomination inside the artificial sun? What’s up with Lag’s mother and why was she taken away from him? If you’re curious about these questions, prepare to be disappointed because rather than answering any of them the production team instead decided to pad out the show with endless, repetitive filler about the “power of heart”. They had 50 episodes (the same as the first Fullmetal Alchemist anime) but somehow ended up with less story development than most twelve-episode series. It somehow manages to rectify this towards the end, but still...