A quiet world recovering from a great cataclysmic event. Level 1 PCs with amnesia.

Fantasy

In the far beginning, ten individuals were chosen to inherit natural power granted to them by the world. These ten were viewed as god-like beings with great power, able to grant boons and brandish banes. Though, their mortal lifespans remained. Every 500 years, the old ten would die, and pass along their power to a new individual.

Unfortunately, getting ten different beings from various backgrounds and ideologies to get along is rather difficult. Eventually, in the previous iteration of the ten, a violent fight broke out amongst them. In their fights, they demolished not only each other but also the world around them. In a last-ditch effort to keep the ten from killing everything, the world itself took back the powers it granted and struck down the ten in localized cataclysmic events.

The next ten were chosen by the world, and then promptly sealed away by the people. These next ten were only to be awoken when their powers become needed. But until then, they slumber under the earth.

Year 0000 - The beginning. The first ten Titans were chosen.

Year 0500 - The cycle. The original ten pass into the next plane of existence, and a new ten take their places.

Year 1000 - The continuation. Shrines have been constructed in a testament to the greatness of the ten.

Year 1500 - The world. Thanks to the efforts of the ten, the world flourishes. Resources come in abundance.

Year 2000 - The war. Various cultures fight over extra resources. The ten abstain from choosing sides, and try their best to quell any insecurities.

Year 2500 - The recovery. Peace leads to healing, and burned bridges get rebuilt.

Year 3000 - The pioneers. Visionaries and curious folk alike expend time and resources into research of magic, science, and technology.

Year 3500 - The people. Folk heroes are being turned to more than the ten themselves. Seeds of discontent spread.

Year 4000 - The doubt. Some members of the ten looked into research of allowing them to live longer, or to even become entirely immortal beings.

Year 4500 - The missing piece. No information remains about this time period, though many theories surround this as the time period which triggered the cataclysms.

Year 5000 - The cataclysms. The final ten were struck down by the world, and the next iterations had been found and sealed away within the world.

Year 6319 - The emergency. The sealed ten get released as an unforeseen threat arises. However, spending over 1000 years in stasis has wiped their memories and reduced them to basic power levels.

Standard

Standard D&D 5e magic system and rules, with some additional homebrew spells and modified spells.

Medieval fantasy

BoTW

Fey - Elf, Orc, Centaur, Satyr, Goblin

Elemental - Genasi, Aasimar, Triton, Tiefling, Hobgoblin, Warforged

Animan - Aarakocra, Kenku, Tabaxi, Shifter, Grung, Dragonborn, Lizardfolk, Kobold, Tortle, Yuan-ti, Leonin, Loxodon, Locathah, Minotaur

Sizekin - Goliath, Firbolg, Bugbear, Dwarf, Halfling, Gnome

Humanoid - Human, Half-Elf, Half-Orc, Verdan, Vedalkin, Kalashtar, Changeling, Simic Hybrid