After all these years and so many great ntr series, it still doesn't get any better than Hitozuma wa Yoitsubureta Otto no Soba de Douryou ni Netorareru by tsusauto HGT LABO
Does anyone remember who made this? It's from a two-parter April Fools swf animation called New Big Change and Real Big Change I downloaded from deviantart over 5 years ago.
