Supreme Dan Refiner of Realms - Chapter 1770 - : Exploring the Mysterious Palace in the Earth’s Core

A series of short stories in the world of Toaru Majutsu no Index organized into chapters featuring Kanzaki Kaori as the protagonist, going around the world and space doing missions for the Church of Necessary Evil, however, there is more than meets the eye as each incident is connected.

One chapter was bundled with each limited edition release of the Toaru Kagaku no Railgun anime DVD and BDs, with all of them together being equivalent to a single normal Toaru Majutsu no Index volume

When Li Shen’s second personality acts out, her consciousness is sent to a strange place called Split Zone No.13. She is then informed that she can only return home after unraveling the truth.

Xu Yiyang, who was only late in his life when he was middle-aged, returned to 1999 in a dream.

At the turn of the millennium and the turn of the century, he realized a truth:
Not only to be famous early, to start a business and make money, but also early!
………………
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- Description from Uukanshu

The story is about a boy entering high school, who answers a strange call from a public phone one night. The caller challenges him to a bet: She’ll remove the birthmark which he sees as the cause of so many problems, and he’ll have fifty days to win the heart of a girl he’d considered far beyond his reach. And with this, a very strange summer begins.