The Kagamine twins are my #1 J-pop artists. They are Vocaloids, and to find more about them, go here: Vocaloid Wiki
You will like their music if you like high-pitched singing, and bright songs. They do a lot of songs together, as well as songs on their own. Here are some examples of their music:

A popular song of Rin's is Meltdown:

A popular song of Len's is Spice:

And a popular song by both of them is Kokoro:

I hope you enjoyed listening to the Kagamine twins!