Shocking! I Started As the Great Black Tomb and Was Immediately Killed

Waking up to find yourself traversing the Star Railway is a joyous occasion, but why are there so many starships around?

After inquiring, I learned that, oh, it turns out I've transmigrated into the Iron Tomb, or rather, the Iron Tomb that has merged with the Great Black Tower. No wonder the perspective is so strange.

Hey, suddenly I felt a chill down my back, a flash of silver light, and then I lost consciousness. Gah, dead!

(Iron Tomb + Great Black Tower = Dark Secret. The protagonist will transform into the corrupted form of the Great Black Tower. Slightly yuri-oriented, OOC, crossover anime, not for those who care about historical accuracy, purely for fun. Please read without thinking and do not take it too seriously.)