Ohh... I remember reading the LN. Only volume 1 was translated at the time, idk about now.
They totally skipped the part where "Nia" fought back against the illness after unvoluntarily dragged into original Nia's body. It was pretty long, so I don't think people would enjoy reading at least 2 chapters only filled with the effort, recovery progress, and mechanism behind "Chi" anyway. It's probably better to explain if bit by bit throughout the story instead.
Also, I heard that a sword might as well be a bat if not swung properly. Idk since I've only ever held a replica, but I can imagine it'd take training to properly slash with a sword.