Kato01's "My demons" is about the pain of hurting someone while fighting a battle inside yourself. The speaker says the demons are something they tried to hide, to keep from "coming out in the daylight," but eventually they won and did damage to another person. Now the speaker wants to say sorry and feels they can't.
What stands out is the sense of being trapped. The speaker believes nobody will accept that they struggled, and that an apology would simply be dismissed. The repeated words, like "tell them" and "believe," echo each other from line to line, almost like someone stuck going over the same worry again and again. That repetition makes the poem feel breathless and anxious.
The mood is guilty, helpless and raw. The last line, saying tears can't show how sorry the speaker is, leaves us with a feeling of regret that has no outlet. The poem doesn't explain what the demons are, so readers can fill that in themselves.