My Space-Time System - Chapter 575 Ironwood Assassination.

She, the “godly doctor” of an assassin organization in 21st century, transmigrated into the body of Yun Family’s abandoned, good-for-nothing Ninth Miss. Good-for-nothing? Then she’ll let the world see what a real good-for-nothing looks like. Summoners are legendary? Nothing is impossible in this world! She’ll become the first Magical Summoner.

He, the third prince in Long Xu Kingdom and the mysterious, behind-the-scenes owner of Zhou Dynasty’s monopolized business, seemingly handsome and uninhibited, is actually brutal and merciless.

The world knows her as a sickly good-for-nothing and her standing is as low as a servant’s, yet she solely dominates his heart. Trickery, schemes, overbearing, seducing… an exhaustion of methods, all to capture her heart. The scheming couple supports each other, producing stories about enmity, love and win-win cooperation.

Read to see how they stand side-by-side at the peak of this extraordinary world.

- Description from Novelupdates

Mysterious gates appeared all around the world a few decades ago. Beings emerged from the gates and brought disaster upon humanity. Humanity called them Demon Spirits. It wasn’t until the advent of Demon Suits and Demon Suiters that humans stood a fighting chance.For some perplexing reason, the world’s number one Demon Suiter, Li “God” Xiu abandons his identity to start over again as a newbie trial-taker. He enters the gates to participate in all sorts of trials, in a bid to seek out the reason that enticed his best friend into becoming a trial-taker.These trials weren't the run-of-the-mill dungeons, ranging from game sports (soccer, basketball, baseball, etc) to athletics. Just as fortune favors the brave, what would Li Xiu obtain on his quest?“Are you telling me he’s a greenhorn?” the other trial-takers frustratingly ask while watching Li Xiu's feats that prove why he's the number one Demon Suiter.

Based on the popular Vocaloid series, by HoneyWorks, called “Kokuhoku Yokou Renshuu (Confession Rehearsal)“:

Natsuki, a third-year at Sakuragaoka High School, who holds unrequited feelings for her childhood friend, Yuu, who’s in the Film Club. However, instead of being honest about her feelings, she makes him be her confession “rehearsal” partner. Unable to say her true feelings, things start to get complicated when Miou and Akari, who are also in the Art Club, get involved! Will she ever be able to confess for real!?