The key i think is to develop things in a way that make sense. And be realist regarding the type of story you are writing. A lot of mangas with red/black flags are presented as either romance stories or dark romance stories. When in most cases they do not have the elements or correct development to be either. Because deep inside, many of them are just abuse abuse, rape etc as an excuse to get into the sexual scenes. Since sex sells the focus is mainly there, so the plot and character development often are all over the place. Most toxic mangas i have read that are supposed to be a dark romance, never explain how or why the characters fall in love. Without a reason, the plot suffers and is impossible to take seriously, because all we usually see is just rape, sex and repeat. So they are more in line with themes of lust and obsession than anything else. Which would be fine, but then the authors should call it as it is. Because there is no romance or dark romance in any of this.
In my many years of reading TOXIC Black Flag stories, the key to not be disappointed with the ending and the lack of redemption, is UNDERSTANDING
Switch your gears like switching songs based on MOODS. Once you understand what these Black Flag characters are, even small acts of kindness will leave you giggling.
What I realized recently is that, I tend to hyper-fixate in comparing FICTION with REALITY. This fixation is what makes me furious. But once you come into an understanding of the Author’s INTENT, you’ll come to actually enjoy reading toxic shit.