I've read this in high school and was able to finish reading it. I actually own the full series (up to volume 10) but I guess I just have to add it to my small collection.
I really enjoyed this series even though I don't normally read this genre. I just wish it hadn't ended where it did. I feel like there was meant to be more but something stopped it from being released or translated or something which is unfortunate because all the secrets were almost out.