They were good friends in their previous life, and became sisters after reincarnation. A few years later, they found themselves in the anime "Guardian Sweetheart" that they liked in their previous life. Later, they also had their own guardian sweethearts, and returned to Japan from South Korea and transferred to Holy Night Academy. Later, K Chair Benri Weishi invited them to join the ranks of guardians and search for embryos together.
Han Yeexi:
Cold Night Painting Theory: