I Became a Girl's Guardian Spirit

He had no name, only the codename Thirteen.

Born with a sword bone and a seven-orificed exquisite heart, he was taken in by the Divine Temple and raised by inhuman methods. He was known as a "weaponized human"!

No family, no friends, no mentors. He killed gods, Buddhas, and the King of Hell, nothing but a killing machine without a trace of emotion.

But one day, an altar appeared before him...

His projection briefly appeared in another world. The one who summoned him was a silly, adorable young girl who claimed to be from Earth and to have transmigrated to another world where guardian spirits were everything.

"Big brother, don't go! Take me with you! Make a pact with me and become my bonded guardian spirit!"

"I have a System! The System said that if the bond succeeds, I'll get a beginner's gift pack."

"It grants guardian spirits a blessing: a true-damage talent that ignores time and space! It even works in your original world!"

"You know what true damage is, right? It ignores defense! It's amazing!"

She thought Thirteen had agreed because of the blessing, but really, he was just bored.

Under the influence of this silly, adorable spirit master, he got a name and gradually transformed from a cold killing machine into a person...

Divine Lord: "Thirteen, what are you doing!"

He didn't answer, only swung his sword...