The three things that qualify for rape, are there tears? No... Is she tied up? yes... Does it look like she's enjoying it? Yes...

Therefore I do not believe that this should be tagged rape.

and I don't believe you've seen this hentai

i don't see much enjoyment on her face neither pain but i think this is pretty obviously rape scene no matter have you seen the hentai or not.

Dude, its a tentacle hentai, rape comes standard its par for the course. Nitpick elsewhere.