“In the beginning, there was an egg, and from that Egg spawned a universe.”
Arceus was born in the void of space as a fletching Arceus. Knowing nothing but the vastness of space and the Unown, she spent her time growing up to slowly discover and hone her skills as a creator. When she seemed to master this power, a strange rift opened, revealing an Ultra Necrozma who took favor of her. Upon request, Arcues married Ultra Necrozma. Necrozma then gave her a name: Izanami, the Invited One.
And happily ever after they lived… for a time. The couple traveled various dimensions, meeting and learning from the native creatures therein. The two eventually settled in Necrozma’s world, where they erected a great throne and gave way for two children: a Solgaleo named Amaterasu and a Lunala named Tsukuyomi. The four lived together in harmony until, one day, Izanami requested to create an entire world to tend to.
Necrozma, infuriated by the request, quickly turned on Izanami, eventually attacking her. While Izanami was ultimately unharmed, her relationship quickly turned toxic and eventually abusive. Suddenly, she started hiding from Necrozma to continue to practice her creation gift, only speaking about it to her children; however, when Necrozma soon discovered her attempts to create anyway, it attempted to kill her. Izanami managed to survive the Necrozma’s onslaught and fled to another world, but not before stealing some Light from Necrozma. Necrozma attempted to chase her, but quickly became too weak to continue and returned home in disgrace.
Izanami stumbled into another Arceus’ world. The Arceus accepted her and vowed to protect her while she was in its domain. There, Izanami rested, becoming a student of the Arceus that took her in. Over time, she learned more of creation itself, the role of Pokémon in the world, and about the humans that inhabited the land. In love with her lessons, Izanami integrated herself as a human trainer in the land to further infatuate herself with this new life. She even found a lover in a Rayquaza soon after she completed her journey.
However, this, too, shall pass in time.
Necrozma eventually found that Arceus’s world and demanded that Izanami would be returned to it. Arceus refused. Instead, Arceus stealthily forced Izanami to leave the realm and declared an all-out war against Necrozma. It was a bloodbath. Necrozma made quick work to overpower and annihilate the world before Izanami could run too far to notice. Thus, fear-ridden and distraught, Izanami continued to flee as she returned to her childhood void. Fearing for her life, Izanami casted a spell in her space, sealing Necrozma out of her realm for eons. Now, with the fear of Necrozma behind her, Izanami created a world of her own filled with humans and Pokémon to tend as her own creating an entire score of Legendary Pokémon to watch over them. Once everything seemed complete, Izanami erected an area for herself to meditate and hone her skills.
Eventually, Izanami became active once more, roaming the lands as a human to learn more of those she protects while dealing with threats against her realm by otherworldly threats. However, there was but one particular individual that she took interest in: Heidi, a Latias that arrived to her world via an Ultra Wormhole. Over the coming years, she prepared Heidi to have the skills and confidence necessary to become her successor without Heidi's knowledge. Then, once Izanami had the confidence that Heidi was ready, Izanami challenged the greatest threat to the world in a duel: Friede, the World Cleanser, an Arceus that threatened to destroy the world.
Izanami lost the duel, and paid for it with her life.
For some time, Izanami rested trusting that Heidi would be able take the mantle; however, through some unknown means, Izanami returned to the world of the living once more. Even though she had a new body and she was newly born, she managed to keep all of her memories and skills. How could this be possible?