"You cannot be my brother—He was cold but he would never have murdered everyone." Fang Zheng spat, he remembered how his brother was, there was only a sharp personality change after their awakening ceremony.
About Wang Er : Fang Zheng would be able to form a small but significant relationship with him, Wang Er directly saying, "If you need anything from the forest tell me and I'll get it."
Fang Zheng should briefly spar with him and only then realize that hes still too weak, Wang Er this way gets a understanding that Moon blades are a thing (forshadow) Wang er Helps Fang Zheng back up and they keep having small interactions, in village markets where there's soft moments of Fang Zheng shopping thinking of what Fang Yuan would like and they just so happen to bump into each other.
After some back and for and back and forth interactions they develop a good enough relationship that when Fang Zheng talks about hunting Wang Er offers to give him a map since he unfortunately couldn't accompany Fang Zheng due to having plans with someone else (this is before he's killed by Fang Yuan)
These interacts will mean Wang Er is harder to kill and Fang Yuan is likely to be injured in the process, this will make it suspicious to Fang Zheng especially who is the most accurate description a vouryier who will in that chapter see FY's wounds and put pieces together,
+ about the situation of entire Heavenly Court x FZ it will be strictly M/M, the female characters affection will go as unreciprocated, Jing Lan or Thunder Ghost True Monarch will be treated as a child/ little girl, like how author would not ship Little Hu with anyone since little Hu clearly has appearance of child, she would not ship a grown man with Jing Lan who has the appearance of a young girl, it goes against the only moral boundary. Primordial origin too because he's ugly asf
Fang Zheng would re-get attached to Fang Yuan after confirming that Fang Yuan has the spring autumn cicada, crying about 'how could i have hated my brother, i should have hated this demon who is wearing his face and deceiveing everyone'
Fang Yuan will suddenly feel the urge to explain himself to Fang Zheng but Fang Zheng won't listen, they fight but eventually Fang Zheng and Fang Yuan come to the same conclusion, Fang Zheng cant kill his own brother, even if its a demon because its still in essence, Fang Yuan with the same body voice and face. (Author likes this trope)
Fang Yuan knows that he should use that opportunity to kill Fang Zheng but he lets Fang Zheng leave with the false reasoning 'I can still use him, Hes still useful.' (Also author k1nk)
But its also because he originally disliked Fang Zheng because Fang Zheng was rude to him first, also choosing to abandon their parents etc, Fang Yuan also originally though Fang Zheng always hated him but always was too weak until their awakening ceremony. (Love miscommunication)
Hearing Fang Zheng confess about his feelings and how he liked 'the original Fang Yuan' despite Fang Yuan being the same person just older.
"My Brother…I know my own brother and he--My brother would never be like you!"
(author hates happiness )