I was playing on the web and i found this article,very intersting!!
Anyway here's the list:

Top 20 Japan’s most wanted girlfriend 2008

1. YUI 2. Kaori Mochida 3. Ayumi Hamasaki 4. Ai Otsuka 5. aiko 6. Ai Takahashi 7. Ai Kawashima 8. Kiyoe Yoshioka 9. Maimi Yajima 10. Yui Aragaki 11. Nocchi 12. Namie Amuro 13. Ayaka 14. Kaela Kimura 15. Kumi Koda 16. Misako Uno 17. Hiroko 18. BoA 19. Mai Kuraki 20. Reina Tanaka

Top 20 Japan’s most wanted boyfriend 2008

1. Jin Akanishi 2. Kazuya Kamenashi 3. Hyde 4. Jun Matsumoto 5. Tomohisa Yamashita 6. Takahiro 7. Takahisa Masuda 8. Jaejoong 9. TAKUYA∞ 10. Sho Sakurai 11. Koichi Domoto 12. Akihito Okano 13. Kentaro Kobuchi 14. Ryo Nishikido 15. Yusuke Kamiji 16. Yuya Tegoshi 17. Masaki Aiba 18. Haruichi Shindou 19. Teppei Koike 20. DAIGO
Koike Teppei is the in the position 19,he should be the first but in an other articlei found he is the the fifth:

01 - Fukuyama Masaharu
02 - Kimura Takuya (SMAP)
03 - Tamaki Hiroshi
04 - Sakurai Sho (Arashi)
05 - Koike Teppei
06 - Domoto Koichi (KinKi Kids)
07 - Kamiji Yusuke
08 - Miura Haruma
09 - Oguri Shun
10 - Sato Takeru


Didi you know that YUI was Teppei-kun's EX-girlfriend,it seems that they brock up four years ago,and a rumor says that he wrote the song Kimi ni ukuru uta for her after thay brock up!! Is this for real??Did you knew about this!!!Please tell me more about this!! I really want to know more and more!!!
Here's Yui


What do you think about her ??Is she pretty ??

omg!!
thnks for the news..!!amounachan!!!
he should be the first...haha
YUI is his 1st girlfren..
i read it somewhere on the net...
but i dunno that he wrote the song for her ..
can neone tell me its rite or wrong..?=|

But why didi they brock up???

huh?
where did see this rumour from, mouna?
snow's never heard of it. xP
=DD

i found it on the internet somewhere ,write down koike teppei's girlfriend in GOOGLE and you will find a lot of people talking about it.

huhu
i thought it was just RUMOR ..
can neone make it clearly ..?T-T

eh??hontou???
I never hear about it...

Yeah me too it's my first time i heard about this taht why i post it

i know this rumor !
BUT IT WAS NEVER TRUE ! .I SWEAR !

this rumor was made by the fans..
they said that the song "goodbye days" was written because she and te-chan broke up but the real deal was it was written for the movie "taiyou no uta".
they also said they broke up because yui is going abroad and she will leave teppei behind ..

that is the whole story ! ..

woah^^
thnk u thnk u thnk u very very very much xammie!!!!!*stammer*
thats a deep relief!!!<3
now i know its a REAL rumor ^^

thank you "xam&teppei4ever" for making everything clear and how could Yui leave Koike Teppei,such cuuute guy!!!!