The moment before William disappeared through the dream tunnel opened by Catherine, just after he spoke his final message, Yi Chen suddenly fell into memories of the past.
He remembered how, at first, he had been imprisoned by William's main consciousness in the aquarium, sealed away in its deepest depths. The aquarium and the library had even been separated by a hidden passage with seven seals in place.
Until one day, William suddenly became proactive. He ventured into the extremely dangerous aquarium and began chatting with Yi Chen through the glass, speaking with him as he remained imprisoned in the deepest part, gradually becoming familiar with him.
After they grew close, William gradually released Yi Chen from his restraints, even taking the initiative to let him walk out of the aquarium.
After the two had cooperated within the body many times, William even took advantage of Silver Turbidity to carve out a special Second Body in his back for Yi Chen to use.
Yi Chen had also helped William cover his eyes when putting on the Abyss Mask. Their relationship grew increasingly intimate, to the point that they were almost like biological brothers.
However,
Yi Chen was not reminiscing because he missed those memories, nor because he was reluctant to see William leave. Rather, he had suddenly noticed several details that were easy to overlook within those "intimate memories."
Especially after William joined the circus, whenever he conversed with Yi Chen in the Hall of Thought, he would unconsciously imitate Yi Chen's behavior, mannerisms, and changes in expression. He imitated the evil Yi Chen had brought from the Orphanage—the evil of a Death Row Inmate from the Prime Material Plane.
Yi Chen even vaguely remembered that sometimes, after William handed over control of the body to him, William would vanish