Check this game if you want old/fat guy raping girl then try these game.
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and these two game by Acerola if you don't mind Ntr'ed.
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and
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Also games from amatsuchiya. I am pretty sure there is fat guy in those game.
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this game too:
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I don't know much about Visual Novel but there should be plenty of Japanese game with those specification.
if you want to play games where you rape fat/old guys well Idk anygame with those things but I guess look at Dlsite(Jp,
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) (eng,
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you might or might not find it. Good Luck.