Martial King's Retired Life - Chapter 6Book 15:

Pain, Pain, Go Away is a novel by Sugaru Miaki, also known as Fafoo, author of Starting Over and Three Days of Happiness. Unlike Miaki’s previous two books, Pain, Pain, Go Away is not a rewrite of any story posted to 2ch, but an entirely original one.

The plot involves a young man who becomes a killer (by accident) – but his victim has the power of “postponement,” temporarily delaying her death.

A side story series featuring the girls of Kyoukai Senjou no Horizon.

Prometheus, the infinite fortress of time, a crossover point for the infinite worlds of machine wars, Our protagonist, Xiao Ran, was put into great pressure due to having only attributes that do not exceed 10, making him as weak as a chicken. But being familiar with the storyline of each mission world, Xiao Ran exclaimed that the world would be his.

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Mission world: “Gundam SEED” -> “Macross F” -> “Gundam 00” -> “Ultimate Mission” -> “Kakumeiki Valvrave”-> “Gundam 0079” -> “Gundam Seed Destiny” -> “Super Robot Wars OG”

- Description from Novelupdates