Any NTR manga or doujin, where the NTR happens in a later chapter.

[dartred]

The manga starts off vanilla. There might be a clear NTR antagonist early on, but he isn't successful in getting the girl. It goes a few chapters or volumes, but eventually NTR does happen.

 

[R18_4DD1CT3D]

I was reading "Boku no Yayoi san" when I remembered this post, I've just read the first 84 pages, there is no NTR until the page 60 and the the manga has 240 pages.

 

[dartred]

i remember that one. one of the NTR classics. a great recommendation.

 

[tracespeck]

Itazura Senyou Hanahira Seitokaichou

Another classic hentai doujin with several vanilla chapters of build up.

And MTSPs famous Tachibana-san-chi no Dansei Jijou Matome Ban has a pretty good vanilla build up