Katahane no Riku was a really interesting series, I'm also surprised that I never found this earlier. Katahane no Riku tells a tale about a red haired-girl named Riku who was born with super-human strength, but thrown away by her family for not being able to awaken her talent as a spiritualist (they're basically people with magic powers who got advantage over demons). As she was on the verge of death a demon reached out to her giving her the choice of siding against her own race or choosing to rot in a back alley where no one will ever care about her. After firmly giving her decision to the demon she grows up to become one of humanity's greatest threats.
Reading the first few chapters I got hooked. After going through 100 chapters in one day (literally stayed up for 24 hours finishing this XD) I experienced many heart clenching moments and many gory, brutal and sadistic scenes, and battles that even sent our adorable Riku to the verge of death, showing us that not all protagonists got perfect lives. Throughout the series Riku gained a lot of compainons and lost some too, but she didn't falter and kept fighting for exacting revenge on her family who saw no worth in her super-human strength.
Anyways while the series is amazing and well written, I have to point out the flaw (s) that was apparent in the series. There was almost no (if not none) character development in the series. All the characters never changed and really felt dull after chapter 70 to me. Another thing I want to point out is the ending. The ending felt so rushed and unsatisfiying, this is actually the main reason why I rated this 4/5, whole the story was amazing but I was seriously disappointed at how the author ended the series. I really would've preferred if he continued it for 1 or 2 more chapters, because I think the way it ended didn't give the readers the feeling that something big happened, and made the reader's think that our MC's story is just one other story that would be recorded in history with various other stories that never stand out (by recorded in history I mean in the novel world's history not real life history).