Seven Sins System - Chapter 3: A Devil Among The Mortals

(Isekai, Fantasy, Non-transmigration, Unconventional, Ensemble cast, Meticulously crafted setting, Multiple identities, Light novel, Succubus)I have many masks, and each has its own story.I am the unremarkable little artist of the Church of Dawn; the strongest apprentice in the gladiator arena; the killing machine in the eyes of goblins... The holy nun beneath the sunlight is me, and so is the old gentleman on the train... I have hurried through underground tunnels in escape, and I have left behind beautiful legends on the frontier...Beneath the mask, there is an even more beautiful mask; within the lie, there often lies a hidden truth...My name is Ogre. A child raised by ogre since birth. It's a pleasure to meet you.

Outer Sect Disciple Chen Yu, assimilates within his body a fiendgod heart.

The heart, is the backbone of life, the human body’s fatal vital point. And it can be said that Chen Yu’s heart is actually his strongest defense point, and permits him to overtake demonic beasts, or divine beasts unlimited potential.

Henceforth, he steps onto the stage and surges forth on a magnificent scale, in a heart-rending mysterious journey.

Talented as a cloud, an unparalleled supreme talent.

10,000 races glorious, cross boundary battles.

Only my heart, eternal!

- Description from Novelupdates

Four years after the Third Nightmare, something unexpected happens. A group of people find themselves in a strange theatre, which tells them to react to someone's story...?

An alien race invaded the Earth on June 6, 2128. At the midst of this war, many nations allied with the alien threat and the war nearly wiped out the rebelling humans of the planet. At the edge of mankind's survival, the United Nations Army launched its forces to eliminate the immediate stellar threats that loomed over Earth.

General Seeker Carlean, commander and leader of the mission, risked and gave his life to destroy the immediate stellar threat. The battle was won though Earth lay in ruins. Perhaps mankind will live to see a few years of peace before the alien threat returns to wipe out their existence.

At the immediate aftermath of the stellar battle, the fallen Seeker Carlean awakens and finds himself at aged 17, living the peaceful life he lived 16 years before he died.

So begins a new game in the battle for humanity's survival.