A Crossover: Starting by Saving Kiana

[Honkai: Star Rail + Genshin Impact + longevity-based card draws + beast taming + original story + expanded shared universe + character training + slow burn] Rong Yao transmigrates to a world of beast taming and awakens a summoning System. He can spend his lifespan to draw cards and turn the characters on those cards into his own spirit beasts! He becomes the only beast tamer of his kind in this world! And so, Firefly, Elysia, Furina... one character after another becomes his to command. The beautiful girls under his command are powerful enough to sweep across the world! The System also provides an evolution feature, allowing him to use precious materials to raise his characters' ranks! From [Glamoth Iron Cavalry] to [Glamoth Empress]; from [Slash] to [Starburst Firefly Slash]; from [Complete Combustion] to [Fireflies Cocooned, Soaring Through Rebirth]! This time, I'll make Firefly truly ignite the sea of stars! From [Miss Fairy] to [Herrscher of Human: Ego]; from [Ice Arrow] to [Arrow of True Ego's Radiance]; from [Pure Love Domain] to [Pure Love Illusion, Flawless True Ego]! This time, I'll make Elysia truly flawless! From [Water God Impersonator] to [Water Archon]; from [Revelry] to [Hymn of the Starry Sky]; from [Judgment] to [Guilty Sway, Verdict Upon the World]! This time, I'll make Furina truly capable of judging the gods! Yandere Firefly: "Rong Yao is mine. He's only allowed to sleep with me, so all of you stay away from him!" Hopeless romantic Elysia: "Rong Yao, do I look pretty today? Will you compliment me?" Silly Furina: "I'm going to judge the gods of the heavens. Rong Yao, I need your help!" By training every character, Rong Yao will eventually become the very end of this world!