He visits her at home, and the father finds out.  The father scorns this courtship, and tells the young samurai to stay away from his daughter and his house.  Both the young mistress and he are distraught and in her grief she commits suicide (that's what it looks like to me, it is also possible she dies, getting ill after being out in a storm, but this is not clear in the film) and visits him a couple of nights later during the o-bon festival (the festival of the dead) they consummate their love, and she leaves vanishing into the fog.

The neighbour of the samurai alerts him that the girl is a ghost, after which he takes steps to protect his house from her.  The young mistress visits again and is unable to attain entry to the house.  So her maid bribes the frightened neighbours into removing the charms from the young samurai's house.

Hellish Love was interesting enough, though I did not find it particularly scary.  Maybe that's because it was in the soft core style and they concentrated more on the sex than they did on the scares.  There are a couple of frights in the film, but not ones that would cover you from head to toe in Goose bumps (if you are lucky enough to be one of the people that that happens to!).

The film is beautifully shot, and does have a  haunting atmosphere to it.   It also contains a weird mix of music, beginning with a plinky kind of Rosemary's Baby (which by the way was driving me mad trying to remember what film it was from!) style music, then moving into something like a Lynchian Twin Peaks style, and then god knows where after that.

The so-called Nikkatsu (a company that specialised in "romantic porno") genre is not one that I am familiar with, this is really my first film in the genre.  I do not know if the genre would include Nagisa Oshima's Realm of the Senses (1976), as it seems like "romantic porno" seems to mean, soft core, and well Oshima's film is certainly not soft core!