This one line from this anime sums up this series well, especially in terms of its story and characters. One thing the synopsis doesn't tell you is that this anime is about learning to be open to new experiences, because life doesn't always go up or down or in a circle.
The character that best embodies this lesson is Kaoru Nishimi, who is one of the main characters and the main focus of this anime. Before he meets Sentarou (a tough, imposing male) and Ritsuko (Sentarou's female childhood friend), Kaoru is an intelligent stiff with social anxiety issues so bad that he feels ill when he feels stressed about interacting with others. Kaoru encloses himself in a metaphorical circle and walks through life with a metaphorical "down" perspective that he gradually comes out of as the series progresses and he learns to play jazz.
Sentarou and Ritsuko embody unexpected directions because of the impact they have on Kaoru and because they aren't what you expect, especially from reading the anime's synopsis. If you have any doubts about this, I recommend watching the first four episodes before you decide to drop this.
The most touching thing about the complexity of Sentarou and Ritsuko is that with Kaoru, they form a deep bond that is like a family. Even when those three are in a love triangle, the familial bond is still there. Despite their romantic feelings, Sentarou is like a elder brother, Ritsuko is like a sister in the middle, and Kaoru is like the youngest brother. This familal bond that causes them to try not to hurt each other and feel remorseful when they do end up doing so.
Besides the characters, the soundtrack is incredible. Composed by Yoko Kanno, the jazz music provides an atmosphere similar to that in Cowboy Bebop, except this jazz isn't bebop. It's relaxing stuff in the vein of John Coltrane (whose work is featured a bit in this anime btw), except during action scenes (which are scored just as well as the stuff from Cowboy Bebop). I downloaded half the soundtrack after watching just the 1st episode, b/c I knew Yoko Kanno would make it great.
The next-to-last notable thing in this anime is the setting. Since it is set in the sixties, a bit of historical and cultural stuff is sprinkled throughout the anime, such as racism, the popularity of rock n' roll (esp. The Beatles), and political student protests. This added depth to the characters' world and made things more interesting for them at times.
Finally, the last notable thing in this anime are little details (probably provided by Cowboy Bebop director Shinichiro Wantabe) such as the episode titles being named after jazz songs, the early love confessions (thank you for not occurring at the very end) and the way music ties the three main characters just as much as their drama.
I've only seen two other music-centered josei anime (NANA and two seasons of Nodame Cantabile), but this one has become my favorite one (sorry NANA). If NANA is the best josei anime with post college grads, then Kids on The Slope is the best josei anime with high school students.
