Reference

Rain decided to test the relic and feed some mana with it, but he only saw the weapon glowing and changing color to blue… he didn't feel anything else. It needed some mana to fire a pretty considerable amount.

"People in the past had this much mana?" Rain furrowed his eyebrows. 

In the end, the weapon had to absorb ten thousand points of mana to be able to fire… at the same time, Rain regretted that a bit since the weapon fired automatically… he didn't even have to pull the trigger.

As Rain saw the relic firing the shot, it pierced the wall of the underwater cave with an eerie silence, an unsettling absence of any typical gunshot noise. The lack of sound was suspicious, especially given the substantial amount of mana that had been infused into the weapon.