I'm a big fan of XXX from China.I came to know about your in 2012.（your-you)
In the <XXX> PV,i think that you are so pretty,and especially cool!I like you and XXX very much.  (此句不通顺,用so ...that可能改善点）

Because of the my japanese is very poor so i can't express very well my total support and adoration for you .( because 与so 不能连用,二者必须删除一个；because of 后面跟的是短语,because 后面才是跟句子的；japanese首字母大写；老外最不喜欢中国人说自己语言poor）

I wish your could do better and better in the future and i'm will alway be your biggist fan who pays attention to what you do all the time.(第一个your-you; i'm-I; alway-always; biggist-biggest)


i sincerely hope that you can write me back.i will be waiting for you.(期待某人的来信习惯用looking forward to hearing from you.)
其实我建议你重写,文章很别扭.
 
能否请你按照我的思路写一篇呢？如果这是写给你偶像的邮件，我觉得直接用你自己的语言会更真实，人家读的是你的诚意不是你的英语水平，努力用自己的语言去表达，不要在乎写得好不好，加油！是作业好吗……汗流浃背，童鞋哎，作业要自己做的好不好，词典呀，单词呀去翻翻嘛