It Seems That I've Slipped Into a Different World. Also, My Gender Has Changed. - Chapter 17: Covertly Assisted, Stealthily Studying

After dying from betrayal, Thomas reincarnates as Jolthar Kaelzhar, the neglected son of a powerful clan, just after his brothers kill him. With Jolthar's memories and the blessing of Qalena, Thomas vows to rise from his lowly position and claim power in his new life.

God's Seal Cathedra Rex, Part Two!Two sons of the dragon, each different; a genius elder brother and a good-for-nothing younger brother, who despite being identical twins, are worlds apart. However, they share an identical desire for peace. On the night of their birth, the moon was high in the sky.

Because her appearance was not breathtaking, the Emperor breaks off their engagement and bestows her instead to the bloodthirsty, ruthless, and cold-blooded Second Prince (Wang Ye).

On her wedding night comes endless humiliation, the genuine Princess Consort becoming a deserted women. A foolish woman before rebirth, she no longer expects his love. In this world, she must possess enough talent to awe those around her, carrying herself with composure and articulating with beautiful diction, override above the nine night.

- Description from Novelupdates

This novel is also known as Gu Daoist Master

Humans are clever in tens of thousands of ways, Gu are the true refined essences of Heaven and Earth.

The Three Temples are unrighteous, the demon is reborn.

Former days are but an old dream, an identical name is made anew.

A story of a time traveler who keeps on being reborn.

A unique world that grows, cultivates, and uses Gu.

The Spring and Autumn Cicada, the Venomous Moonlight Gu, the Wine Insect, All-Encompassing Golden Light Insect, Slender Black Hair Gu, Gu of Hope…

And a great demon of the world that does exactly as his heart pleases!

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*Gu (蛊) referred to poisonous insects in various cultures in South China while in folklore Gu spirits could transform into all kinds of species.

- Description from Novelupdates