kankaku shadan
A fetish consisting of an character falling into a tentacle pit and having their senses (= kankaku in Japanese) cut off (= shadan) usually by either magic or paralyzing poison, while being ravaged by tentacles while being completely oblivious to the fact due to the cut off senses. Often includes a follow up where the sensory nulling ends for one reason or another, which causes the victim to be forced to feel intense senses of overwhelming pleasure all at once. Breast expansion and inflation are often present as well.
In rare cases when tentacle pit is not involved but the setting is otherwise similar, the tag is still applicable.
Originating from post #6364507, which also gives the fetish its name.