Koukousei WEB Sakka no Mote Seikatsu: "Anta ga Kami Sakka na Wake Nai Deshou" to Boku wo Futta Osanajimi ga Koukai Shiteru kedo Mou Osoi

Agematsu Yuuta is the author of the most popular web novel of the century—and he’s only in high school! With such a huge hit under his name, he finds himself the target of affection from people like a beautiful editor, an idol singer, and a popular voice actor! However, Yuuta’s main goal is to win over his childhood friend through a heartfelt confession...and things take a very unexpected turn!

A rom-com about cute girls competing for a best-selling author.

(Source: Manga UP!)