The story is a 10, up till the last chapter. while its heavy and hard to read, it was a very good plot and, besides the last chapter, it felt fullfilling and right.
Art, in my opinion, is an 8. I believe the perception of art varies from person to person, and althought the manga panels themselves are beautifully drawn, i felt like only the static images deserved more than a 7.
The characters are well drawn and their emotions are well depicted, but by the end of the manga, i felt as if both of them were strangers to me and to each other. Both of
them had no real character development, but seeing them blend into a single, awful entity was intriguing.
As far as enjoyment goes, "Itou-san" was a perfect cath for me. I enjoy dark stories about people with wounds, and i enjoy it even more when things feel real. Personally, i found both characters awful people, and the end, although anticlimatic, was a perfect ending for such scums.
Overall, its a 9, with indulgence. I have rated evrything in an objective way, making sure not to let my respect for the mangaka bias me.
Take this as a trigger warning: heavy rape, sexual violence and poorly depicted and unhealty BDSM.