Marked Ones: Advent of the Demon Prince - Chapter 304: Mountain and the Forge

The main character is reborn as a character from a game he played in his previous life. This character falls into ruin along with the villainess, spending the last of their years together. A man named Kururi Helan.

After a tear in reality pulls Kagari Shuya into a white room he discovers a futuristic interface for reincarnating in a different world. After looking through the different races and skills he unlocks a new race, Lucivault, a type of vampire with none of its characteristic weaknesses. All set to start his life in a new world, Shuya is confused to discover that he is enveloped in darkness. As it turns out something went wrong when he was transported and instead of appearing where he was supposed to, he appeared in an underground cave. Shuya faces untold dangers, runs for his life, before finding his way out of the underground world. After escaping he meets his Shishou and begins to learn to fight with a spear. There is also a cute black cat named Rollo.

I am Master Siwei, and I speak for arcane arts.
This is an era of heroes and heroines.
This is an era of great changes.
In the end, it will be an arcane era opened by me.

- Description from Novelupdates

...[Inside an underground basement]“You are going to die for nothing, hahahaha,” the old man's voice thundered through the room, sending chills down my spine.Step.With a swift and ruthless motion, he lunged forward, his sword slicing through the air and slashing my throat, crimson droplets staining the darkness.“We'll see,” I whispered defiantly, my final words escaping as a mere breath against the impending darkness.Slowly, inexorably, my consciousness slipped away, and I descended into a deep, unfathomable slumber.“Huh!?” My eyes fluttered open, and I found myself seated in a bustling tavern, the air thick with laughter and the clinking of glasses.In front of me stood a captivating lady, her beauty juxtaposed with an angry furrow upon her brow, threatening to shatter the harmony of the jovial scene.“Don't follow me around!” Her words pierced the air like shards of ice, the intensity of her emotions palpable as she cast a resentful glare in my direction, before swiftly departing from the tavern....Am I trapped within the confines of a game? The fragments of my shattered common sense scattered before me, leaving me to question the very fabric of my reality.