basically what happens in lucent historia from what i can understand is

ok so first off arcaea is this afterlife that works as like heaven for some people, arcaea gives these people a new name and style and it kinda like changes their entire personality

and in arcaea's act 1 finale tairitsu (a shaper) dies and hikari (the one who apparently created arcaea without knowledge) revives tairitsu using a huge chunk of what keeps arcaea stable to revive tairitsu

tairitsu is apparently a shaper and in doing so they had their soul split into two when they first entered in arcaea, so im pretty sure thats why hikari was able to revive them in the finale

in LH its revealed to be a god named lephon who is apparently dead because he was killed by shapers, although theres this thing called "lephons sphine" which is iirc smack dab in the center of the universe, with these golden strings expanding to other planets and whatnot

and lephons sphine is supposed to like keep all the planets safe im pretty sure

and the shapers are still a thing, im pretty sure theyre like nominated by lephon himself by like hearing his voice 

and so lacrymira (dubbed L for like half the story) and nell (L's mentor and apparently sister) one day are told that the 2nd shaper (faith) is going to break lephon's sphine and so nell and L go over to stop faith

(also L has like. powers or something idefk)

nell stops faith and gets nominated by lephon as the 8th seeker (compassion), and while that is happening faith and nell are still fighting, faith grabs L and chops off their entire arm and then uses the opportunity to kill nell, apparently L stops time shortly after and goes insane, breaks into lephon's sphine and like speaks to lephon and gets nominated as the 8th seeker instead (insight) and is apparently dubbed as the "new god" since lephon is dead

and then resumes time, kills faith, and then flips off nell nominating them as the 6th shaper (forlorn) and then dips via some random portal that appeared outta nowhere idek

and then in act 2 part 1 L like enters arcaea and kills a dude or two or three