"Shinyuu Mob no Ore ni Shujinkou no Imouto ga Horeru Wake ga Nai" is a light novel that tells the story of Kou Kunugi, a high school student who used to be a hero in another world, and his best friend Kaito Ayase, who is a charming and good-looking boy with a harem of beautiful girls. Kou supports Kaito from the shadows, trying to help him win the hearts of the girls he likes. However, their plan is threatened when Kaito's little sister Hikari Ayase appears and seems to develop feelings for Kou. The light novel is a romantic comedy that explores the dynamics between friends,family, and romantic interests. The characters are well-developed, with distinct personalities that complement each other. Kou is the ultimate wingman, always putting his friend's happiness above his own, while Kaito is the quintessential rom-com protagonist, with a charming personality and good looks. Hikari is the wildcard, bringing an element of unpredictability to the story.

The plot is engaging, with plenty of comedic moments that will make you laugh out loud. The interactions between the characters are entertaining, and the romantic tension is palpable. The writing is easy to follow, with a good balance of dialogue and narration.

However, the light novel suffers from a lack of originality. The story follows the standard rom-com tropes, with little deviation from the formula. The characters, while well-developed, are not particularly unique or groundbreaking. Additionally, some of the plot points feel contrived, and the pacing can be slow at times.

Overall, "Shinyuu Mob no Ore ni Shujinkou no Imouto ga Horeru Wake ga Nai" is an enjoyable light novel that delivers on its promise of a romantic comedy. While it may not break new ground in terms of storytelling, it provides a fun and entertaining read that fans of the genre will appreciate. Therefore, I would rate it a 7/10.