MTL - My Girlfriend has a System - Chapter 223 Amazing battle! (3000 words large

A spin-off of the various works of Kamachi Kazuma. One day, Kamijou Touma (A Certain Magical Index) faced yet another misfortune. His toilet was broken and spraying water everywhere. As he was lamenting his misfortune, suddenly he appeared in a strange place along with Index and Misaka. Soon enough, more strange people begin appearing…

Includes:

A Certain Magical Index

Heavy Object

The Zashiki Warashi of Intellectual Village

The Circumstances Leading to Waltraute’s Marriage

A Simple Survey / A Simple Monitoring

Killer Princess and Deep End

Live again, earn money well, and live life slowly. General group: 841193493

- Description from novelbuddy

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

In the beginning, when they all thought that she was “he”….

ML #1: We will be brothers for life!

ML #2: This time I’ll reluctantly let you have the #1 seat.

ML #3: I will properly repay royal teacher!

ML #4: Ah Rong is my closest little brother, I trust him.

Afterwards…

MLs: I’m seriously such a fool.

MLs: What do I do, I think I’m gay. I fell in love with my bro/rival/teacher….

Afterwards….

MLs: I’m straight! As straight as steel!

Note:
MC is a girl crossdressing as a boy, she knows how to fight, and naturally possess the gold finger halo from the author.

All the ML(s) is the same person, 1v1, sc, HE

- Description from Novelupdates