There are more events which add affection with natalie. You might need to be her girlfriend for this.
SPOILER
Once you're back from earth you can trigger the second dinner together with Julie the merchant and natalie for +1 affection.
Intimate scene in the bedroom for another +1 affection It also unlocked other bedroom scenes.
Have the transformation unlocked with Erica. You can do two bedroom scenes with natalie in this form which add at least +1 affection.
There are also bdsm scenes with natalie which dont add affection but can unlock you the succubus form.
Break into Yoshidas bedroom and take a look at the items inside.
Inside Marianne's office room is a naughty photo album.
Pleasure palace bedroom in the top left has toys on the bed.
bdsm magazines from the office building. I have no memory where i got it from but natalie speculated it belongs to either Marianne or Olivia.
There is also a wet dream version which isnt part of the bdsm series. Inside the phyrres tower on one of the bookshelves has a book which gives Natalie a nasty idea. It doesnt add any affection.