The first Japanese songs I heard were "Moonlight Densetsu" and "Ai no Senshi" from Sailor Moon, in around 2000 or early 2001.
The first "mainstream" Japanese artist doinkies heard of was, oddly enough, GLAY. I ended up on a GLAY fansite once and thought "Guys wearing makeup? Interesting", and started looking for their songs. Well, though I did find some songs of theirs, I ended up stumbling onto tons of other J-pop mp3 download sites and ended up downloading other songs too like "Audience" by Hamasaki Ayumi, "For You" by Utada Hikaru, "Amazing Kiss" by BoA, "Ai no Kakera" by Every Little Thing, "Seven Seas" by Aikawa Nanase...etc. And I discovered H!P on one of these sites, the somewhat misleadingly-named "Fantasy Palace", which was a Korean site (IIRC) that put up the then-new singles and albums for download. I first downloaded Renai Revolution 21, Pittari Shitai Xmas, Yaruki! It's Easy, Popcorn Love, and Futari Gurashi, and doinkies enjoyed these songs so much that I started looking for more songs by MoMusu, Pucchimoni, Goto Maki, and Nakazawa Yuko, and along the way I discovered that these artists were all related, under the same management, and that Maki was a member of MoMusu and Yuko used to be. That led me to find out even more about H!P and J-pop. And now doinkies never listens to GLAY or J-rock anymore, there are so many other interesting singers and groups in the J-pop world that aren't guys wearing makeup
