Mujou no Erasmus - The Erasmus two-faced stories

First story:

One day, Mell receives a mysterious e-mail from someone who signs themselves as the “Witch of Fog”. The Witch has organized a class reunion for him and his former roommates who all attended Erasmus in Strasbourg together.

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Second story:

Ten years before the first story, Michel receives an e-mail from Neige, his e-mail penpal he has met on an online suicide community. She wonders whether he really exists in this world and asks him to meet in Prague the day after tomorrow.