[Lore Concept] Holy Lunar Prison

Many thousands years ago, when people of Valoran just started building villages, god of the sun and god of the moon were close friends. They build a temple on the moon. However, temple was more like a prison, than a temple, because those two gods captured and imprisoned many wild spirits and immortal creatures, locked them away in this lunar temple. This prison sucked away the magic of prisoners, mixing it with light of the sun and rained down it to the world bellow, thus allowing people of Runeterra practice lunar magic. Over time, while two gods worked together, they even made the Sun Disc in the lunar temple and carried it down to Valoran, symbolizing power of two gods and gathering light of the sun and magic leaking from the moon.

However, two gods had an argument and fight between them started high above Runeterra. Sun god won and imprisoned moon god in the lunar temple alongside of other spirits and immortals. During this time, people of Valoran, who worshiped moon god, felt that their god was defeated, so they abandoned their faith and started to worship the sun god.

Lunar prison, now left unsupervised, was slowly crumbling down, releasing more and more stored magic down to Valoran. This increasing in magic cause many different things to happen. Ancient monsters awaken, celestials starts visiting Valoran, wild spirits morphs into physical forms and much more. Also, many imprisoned beings, including moon god, started to break free out of this prison. Some run away into deep space, away from Runeterra and sun god. However, some descended into Runeterra. What they want and what they will do remains a mystery, but one thing is certain: a new war between the gods are closing in. The forgotten god and the light bringing god will face each other once again.