Man, love this girl, pity that aren't many hentai and the majority is like this. Kenichi manga and anime came just before internet got big, so even if it did get more works in Japan they are lost as no one updtaed them, and knowing the art quality for most doujinshi in 2005 we aren't really losing too much. Is a pity that Kenichi was released back then as no ne will do much for it today, and the other works from that mangaka have the same quality of girls, very nice, but aren't popular enough.
Ken'ichi's manga came out in 2002 (finished in 2014) and anime in 2006 (the show finished in 2007). Naruto's manga came out in 1999 (finished in 2014) and the anime in 2002 (finished in 2017, not counting Boruto). One Piece's manga came out in 1997 and the anime in 1999, both are still ongoing. Plenty of Naruto and Bleach doujins.
The series' release is irrelevant. There were never that many doujins because the series was not very popular, but there were still quite a few that were posted here over the years.