Re:Zero Kara Hajimeru Isekai Seikatsu - Chapter 60Arc 7, - “The Planting of a Tumultuous Seedling”

Qin Chen was transmigrated to the Taiyi Holy Land where he became a servant in charge of sweeping the floor. However, on his 16th birthday, he was rewarded with a system where he was rewarded whenever he signed in at a new place.

When he signed in at the Empire Ruin, he was rewarded with the strongest Chaotic Holy Body and the Chaos Emperor Scripture.

When he signed in at the Demon Sealing Land, he was rewarded with the Probationary Royal Armies.

When he signed in at the Alchemy Palace, he was rewarded with the Divine-grade Alchemy.

When he signed in at the Herb Garden, he was rewarded with an Immortality Elixir.

When he signed in at the Empire Palace, he was rewarded with the Emperor-grade Divine Art, Revival.

…

Qin Chen thought he could just spend the rest of his life signing in at different places until he became invincible.

However, when the ruin of the Great Kingdom appeared inside the holy land, people from other holy lands, prestigious families, and even ancient empires gathered to defeat the All-Powerful Demon King who appeared with the ruin. The Demon King had killed countless people and had planned to destroy the Taiyi Holy Land.

Qin Chen was left with no choice but to step up. When he killed the Demon King with a single slap, he sighed, “Why do you guys have to force a mere servant to act?”

The world of Nyil, with its monsters, its knights and its mildly sociopathic gods. Come and see! A soul flees and a soul arrives, blessed by luck. Will she survive? Will she thrive? Will she become a calamity? After all, luck is such a fickle thing. ‍

In novels with a stud there is always a Senior Martial Brother like this:

In the early stages of the novel, his innate talent is high, his cultivation is good, his appearance is handsome, and he has an intelligent, cute younger Martial Sister as a fiancée.

In the middle stages of the novel, he is caught unprepared and defeated by a young disciple (the protagonist) in the sect who’s hardly remarkable at all. From then on, he falls from his godly altar and loses his brilliance. Even his young Martial Sister leaves him for someone else.

In the late stages of the novel, he continues to turn dark, going down the Demonic Path and becoming the major villainous boss. However, the protagonist still ruthlessly defeats him and his soul is eternally sealed.

Once Qin Mo opened his eyes, he discovered that he had become this Senior Martial Brother.

- Description from Novelupdates

“O, Hero!” With that cliched line, Kazuya Souma found himself summoned to another world and his adventure–-did not begin. After he presents his plan to strengthen the country economically and militarily, the king cedes the throne to him and Souma finds himself saddled with ruling the nation! What’s more, he’s betrothed to the king’s daughter now…?! In order to get the country back on its feet, Souma calls the wise, the talented, and the gifted to his side. Five people gather before the newly crowned Souma. Just what are the many talents and abilities they possess…?! What path will his outlook as a realist take Souma and the people of his country down? A revolutionary transferred-to-another-world administrative fantasy series starts here!