The light novel series you are looking for is titled Kanojo ga Senpai ni NTR-reta node, Senpai no Kanojo wo NTR-masu (translation:

The Light Novel series is ongoing/completed in Japan with multiple volumes. The original Web Novel on had over 95 chapters as of late 2022. Drama, Romance, Revenge, Netorare (NTR) / Netori. Plot Summary The story follows Yuu Isshiki , a college student who discovers his girlfriend, , is cheating on him with his popular and wealthy "senpai,"

Heartbroken but fueled by a desire for retribution, Yuu contacts Kamokura's own girlfriend, a beautiful and refined girl named Touko Sakurai

. Yuu proposes they get revenge by "cheating" with each other to spite their unfaithful partners. However, Touko suggests a more strategic and public "social" revenge rather than just physical infidelity—leading to a secret alliance to gather evidence and expose the cheaters. Key Characters Yuu Isshiki:

Kanojo ga Senpai ni NTR-reta node, Senpai no Kanojo wo NTR-masu Shinden Mihiro

The "Senpai's" girlfriend. She is sharp, composed, and the mastermind behind the specific revenge plans.