What's the song usually used on the most intense parts and most cool parts in Eureka Seven? I'm looking for a specific song from the soundtrack of Eureka Seven, but I'm having a hard time finding it.

The song plays usually during the most intense parts and most cool parts of the show, like when something whimsical happens. The song has vocals and is very smooth to the ears.

An example is in episode 6, a song with a really nice guitar riff and vocal around 14:16 minutes in. It's like J-rock.
I think the song you are looking for is Storywriter. It's the main theme of Eureka Seven. You can find it on youtube very easily by searching "Storywriter". Don't hesitate to go further in the song because the beginning can be misleading.