A Mastermind? No, I'm just the Live-In Son-in-Law - Chapter 48: Misunderstanding

An Imperial Scholar by day. An assassin by night.The World of Cultivation has changed.Elemental Mancers. Flux Mancers. Spirit Mancers. Soul Mancers.Raining down fire and splitting oceans. Destroying mountains with a single stomp and calming skies with a glance. Controlling the tides of Karma, while wielding the souls of others like a puppeteer tugging on the Lines of Fate.The most mysterious of them all were Spirit Mancers, a truth that Theron was more than intimately familiar with. Due to one's Tribulation, his life was turned upside down. His family, his rage, his somber sadness becoming nothing more than Bad Karma's fuel for a madman.He was once a gentle young man, a non-combative Water Mancer who wanted nothing more than to read his novels to the sound of the rain and one day become an Imperial Scholar.But now...Everything had changed.He donned a cloak in the silent night as the clouds above gathered. Pulling its hood over his chilling blue eyes, he stalked off into the darkness.The first droplets fell.He would become the nightmare of his enemies, the blade hidden in the shadows of Heaven's tears.The River of the Night.

After successfully reaching the Core Formation Stage and forming his Golden Core, Bai Langtian was betrayed by his own Master. His core was ripped from his body, and he was thrown off a mountain cliff into a valley full of demonic beasts.Thankfully, he survived the fall, and met his senior sister, Shangguan Yue Ling.She too had been betrayed by the same Master and pushed into this valley ten years ago. Ever since, she had been surviving alone by eating the corrupted flesh of demonic beasts.Now, Yue Ling revealed to Langtian a new path of cultivation:Demonic Cultivation.To reclaim his strength and take revenge, he must consume the flesh and essence of ten thousand demonic beasts.

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- Description from Novelupdates

Side story of Kyoukai Senjou no Horizon bundled with the first press release of the 1st, 3rd, 5th and 7th Blu-ray volumes of both seasons of anime.

This side story follows Asama, Kimi and Mitotsudaira aboard Musashi one year before the beginning of the main story, as Asama is considering to create a music band together with her two friends for the next festival in Aki, a territory under the governance of K.P.A. Italia.