Koizumi-san is a reserved and mysterious high school girl. Her classmate Ohsawa Yuu is very interested in this new transfer student. One day on her way home, she happens to see Koizumi-san in a long line in front of a ramen shop, which leads to them eating ramen together, and yet...

Nakamura Misa was supposed to go on a date, but instead her boyfriend dumps her without giving her any recourse. Misa spots Koizumi-san walking by and shadows her, thinking that she might have seen the embarrassing scene. Her destination seems to be a red ramen shop specializing in extremely spicy ramens...

Once again, Koizumi-san cooly declines Yuu's invitation to go eat together, but giving up is not Yuu's style. The two of them actually meet at a ramen shop, but it's jam-packed and there are single seat cubicles and Koizumi-san could not be further away! However, Yuu's going to have her moment in the sun where she gets to flex her cooking chops...

One day, Koizumi-san leaves school saying that she has something to do. Yuu is doesn't think anything of it, sure that she is talking about ramen again. But of course, Yuu tails her again, and she sees Koizumi-san waiting for someone in front of a fancy western restaurant. When a dashing man appears she yells "Koizumi-san, don't!"

In today's science class, the four girls learn about the 'green bug' which is known as euglena. Brimming with scientific curiousity, Jun can't stop wondering about what that might taste like, and agrees to go have euglena ramen with Koizumi-san. What is that absolutely foreign flavor going to be like???

The summer heat is on! Koizumi-san looks at the trio loudly suffering from the heat with disdain while she continues on her ramen pilgrimage. Yuu wills herself to follow her, and Koizumi-san declares that she will be having "hiyashi" ramen. What exactly is this "hiyashi" ramen?

Now that summer break is upon them, the trio try to come up with a plan. Koizumi-san already has an answer for that, which is to travel all over the nation. Koizumi-san is finally going nationwide?!

Yuu and Misa are fully enjoying the gifts of summer at the ocean. On the other hand, Jun is in the library working on her summer homework because she's too embarrassed to wear her bathing suit. Jun's agonizing about the report she's supposed to write about her future career when she happens to meet Koizumi-san and asks her about her aspirations. What could Koizumi-san's dream be?

Mountains. They proudly stand tall in the land and thwart man's efforts. Mountains. Mysterious places that continue to produce solemn silence. Mountains. They challenge man to reach for the stars. "Reaching the summit was not my goal" -Why does man, why does Koizumi-san climb mountains?

Yellow... Blue...? Soy milk...? Milk coffee...!? Alkali!? "Today, Koizumi was eating some kind of water-colored ramen." Ramen is... the universe.

Yuu tries to recreate the ramen of her childhood. She can't even remember the name of the place, and with only the fact that it's "Delicious Ramen", she is a complete loss. However, after Koizumi-san samples her ramen, they figure out the original source. What exactly is the mysterious "Delicious Ramen"?

Yuu was on the train from Osaka to Tokyo, but when she senses Koizumi-san's presence, she leaps off the train in Nagoya... She then loses sight of Koizumi-san and only has a 500 Yen coin to her name. Slightly faint, she enters a ramen shop where she can eat something that one coin...