 If you liked
Euphoria
|
 ...then you might like
Kowaku no Toki
|
if you're looking for some hardcore stuff, like dark, makes you question your sanity, has a large shock factor and some plot, material then both are extremely similar. one can say that these are akin to sexual torture.
sure, you could be pointed out to other anime that have tentacles but neither of these use those cliches, they present situations that are impressively far worse.
not for the faint of heart