Toaru Majutsu no Index: Genesis Testament - Volume 1, Afterword

He crossed over to a new world where humans have magical power. They are called warriors. They use their power to kill the monsters that appear out of nowhere. Dragons, Dungeons, and Magic users are pretty common in this world. If you want to live in peace, you need to have that power. You can also become a powerful clearing dungeon.

In this dangerous world, he has a system that can help him grow stronger. But he didn't want to be a high-profile warrior who attracts much powerhouse attention or become a lab rat. He wants to be Low-profile and grow strong using his system.

Gu Zuo: Are you sick?

Gongyi Tianheng: You have medicine?

Gu Zuo: You’re sick!

Gongyi Tianheng: If I say I’m sick, can you cure me?

Gu Zuo: If I say I have medicine, would you want it?

Gongyi Tianheng: However much you have is how much I want.

Gu Zuo: However much you want is how much I have.

Gongyi Tianheng: Then bring it all out.

Gu Zuo: …

Simply speaking, a scaredy-cat shou transmigrated and had to think of a way to survive. He had a golden finger called Medicine Refining System, but unfortunately, he didn’t have the ingredients needed to refine medicine and level up.

A great young master to an Empire’s preeminent Clan had a super high IQ, but his talent for cultivation was low. Unfortunately, pill refiners were too hard to develop, and weren’t restricted to his personal service. But he could acquire plenty of ingredients.

Two people, one was sick and one had medicine. Therefore, the one who was sick kept the one who had medicine, and everyone was happy.

- Description from novelupdates

A mysterious teenager who had lost his past, awakened in Tianlong Continent. Mistaken as the Ye family’s Son, he used this identity to observe this chaotic world and to search for his past self, but only to find an inevitable and terrible fate, therefore he indignantly laughed at his destiny, and revealed his prowess to rule the lands under the heavens.

After 20 years of dedicating his life to opera ever since he had quit the performing arts high school, he had failed at an interview. Losing his motivations, Jo Yunjae depended on alcohol to live out his days until one day, he had been sent back 20 years in time, to the day before his high school admission.