Many years ago, while browsing forums, I came across this particular site.
And more specifically, a game. Try as I might, I can't recall its name, nor have I found it through searches.
It was sort of guro, but on the lighter side (by which I mean that the unfortunate victim, by the end, was still sexually appealing to someone who might not be into this stuff). The torture featured beating, electrocution, dipping in hot liquid and tentacle rape. That last part makes it lost into a sea of so many thematically similar games. The closest I could find (within that approximate timeframe) was Lapis Gunner, but, while similar, that is so not it.
Indeed the plotline was about this sci-fi fighter (maybe Star or Defender was in the title) blue-haired girl who wanted to rescue someone. But in this particular game it was a sister. There were just 4 characters: the evil alien tentacle emperor/empress, his/her underling, the blue-haired girl (that inevitably got caught) and her already-imprisoned sister (which was blonde). You played as the underling (also female and also with tentacles) trying to break the caught girl into submission. There were a couple of different endings based on the punishments chosen. The animation was very good, but that may be just a subjective opinion.
There was also a mini game in between scenes where you had to fight the girl trying to escape (by blocking her pistol/energy shots while breaking her defences/shields? -- via proper timing).
Later Edit: Other distinctive traits were the fact that most of the torture mentioned above involved usage of tentacles or similar appendages. One ending, I believe, involved penetration by a conical drill-shapped tentacle.
Any help in identifying the title would be appreciated.