Urasekai Picnic - MangaDex

The story is set in the modern world, but there exist doors that can take people to the "other side," where strange urban legends and internet stories prove to be true. College student Sorawo Kamikoshi finds herself exploring one of these doors, and almost dies on the other side, when she is rescued by another girl named Toriko Nishina. Toriko is a mysterious girl, but very skilled with a gun, and she seems to be searching for someone else on the other side. Together, both girls start to explore these doors to the other side.

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Urasekai Picnic - MangaDex

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Urasekai Picnic - MangaDex