Mysterious Savulune

Mysterious Savulune (不思議なサヴルネ) is a fictional science fantasy manga often mentioned in the later entries of Innocence Seekers: The Black Rose. In-universe, its author is Inori Akagawa, and it was first serialised in 2015. Published monthly (due to the author's other commitments, such as school, drawing light novel illustrations and performing assignments for the Zodiac Warriors), it received an anime adaptation in 2019.

Story
20XX, Tokyo, Japan. Yume and her two friends, Hotaru and Nanami, were walking home from school when they came across a mysterious object in the middle of a park. When the three girls went up to the object, it suddenly activated and teleported them into a strange, futuristic structure. Not knowing what had happened, the girls looked around the strange place to find any way back home, but only found other people, seemingly trapped as well. After speaking to the other people, who called themselves researchers and explorers, the girls found out that they were located in a different galaxy, which the people within the structure called "Savulune", and that the only two-way link between Savulune and Earth had suddenly closed a year ago, leaving the researchers and explorers trapped.

During their time in Savulune, the researchers had made an unusual discovery. The advanced civilisation that once inhabited the galaxy had mastered the use of a strange phenomenon, one that could revolutionise human civilisation back on Earth. The explorers called it "magic", but the researchers tended to avoid that word. Regardless, it appeared that the ability to use magic was limited only to a few individuals, and none of the researchers and explorers could use it. However, Yume and her friends managed to induce a response in a magical artifact owned by the researchers, something which no one else had been able to do.

This amazed the researchers. They thought that maybe the civilisation's ruins were waiting for a human who could use magic, and that the massive influx of humans who could not use magic may have indirectly led to the closure of the link between Savulune and Earth. Therefore, they thought, Yume and her friends were chosen because of their ability to use magic. But for what, no one knew. That is something for Yume and her friends to find out.

Main characters
Yume Usami (宇佐美 ゆめ)

Yume is the main character of the story. At the beginning of the story, she is an ordinary fourth-grader, one of many people completely unaware of the existence of Savulune. However, her life changed forever when she and her friends came across a mysterious object that transported them to a strange place.

Hotaru Izawa (井澤 ほたる)

Nanami Hoshikawa (星川 ななみ)

Trivia

 * The "X"s in the year are deliberate.
 * Inori has stated that she authored this manga because people started associating her with Kimura's light novels, which are typically fanservice-heavy harems (note that very few people know that Kimura is, in fact, Inori's brother).
 * The three main characters were, according to Inori, based off her friends. While no one knows exactly which of her friends inspired which characters, a common guess is that Yume = Akari, Hotaru = Yayoi and Nanami = Mirai.