...Seishunchuu!

From Impossibility:

Kiriko has always been overshadowed by her older sister Eiko. Eiko is cute, smart, and extremely popular, unlike Kiriko. This manga is about Kiriko leaving her sister's shadow. Although this sounds like a typical manga, the manga-ka enjoys switching to different manga styles to show extreme expressions and actions of the characters. Seishunchuu is a very cute and funny manga!