I first heard of loli hentai when reading, "Memoirs of a porn store clerk" or some such similar blog- it would have been sometime in 2001-2002 (I recall what I was doing schoolwise- but not when in the year). However, I didn't really look into it beyond looking up hotties from videogames/anime.
My first actual exposure was probably around 2005 from downloading "The Story of Little Monica", which was appealing enough to fap to, but always made me feel really dirty afterwards.
My real appreciation for loli came shortly after my exposure to wincest, when I realized that younger sister sex was comparably hot to older sister sex, at least when done in the format of exporation gone a little far. In particular, "Together with Brother" by Kisaragi Gunma, from the Love Selection tonbouken is what really turned me onto the stuff.
(bringing loli to the masses)
http://g.e-hentai.org/g/36416/cfb2d64b5e/

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