Obviously, Gabriel and baby Castiel are the main characters. Gabriel is the one who leaves, and baby Castiel is the one left behind.
There could also be other secondary characters. Maybe some angels or humans who become involved in the situation after Gabriel leaves. For instance, if the story is set in the Supernatural world, characters like Sam and Dean might make an appearance and play a role in baby Castiel's life after Gabriel's departure.
In addition to Gabriel and baby Castiel, there might be some angelic beings that are related to Gabriel. They could be part of the backstory that led to Gabriel's decision to leave. And who knows, there might be some new characters created specifically for this fanfiction to add more depth to the story.
If you want the clearest chapter reference, go to Chapter 151. Early on, Now it was Zhang Cheng's turn to be confused.; later, the chapter leans on The problem lies with He Yun?. By the close, I will have my assistant pay the bill., and the chapter closes with Was he...
Look to Chapter 120 for the clearest answer. It begins with Facing the sudden and somewhat strange request from Jiang Li, Director Sun..., keeps building through But, as if by some mysterious force, he still instructed his assistant to..., and lands on Drink this." Wen Jiaojiao looked at the half.
Chapter 117 is the strongest chapter-level answer because it starts from Fragrant and cloyingly sweet potatoes and corn were out of the pot, and Qi... and follows through on Since entering puberty, his mother had exerted strict control over his....
Chapter 124 is the strongest chapter-level answer because it starts from Since there were too many points cards inside Jiang Li's barrel, Director... and follows through on No need to repeat that number three times.] [Hang on, didn't Jiang Yan....
If you want the clearest chapter reference, go to Chapter 110. Early on, Jiang Li, carrying a wooden basin, walked over to the well.; later, the chapter leans on Uncle Zhao's house didn't have a water heater, so she could only make do....
If you want the clearest chapter reference, go to Chapter 93. Early on, Jiang Li looked back and saw several aunties linking arms, walking up the...; later, the chapter leans on The leader was indeed the aunt to whom she had read fortunes this morning..
If you want the clearest chapter reference, go to Chapter 126. Early on, Wen Jiaojiao initially wanted to cause trouble.; later, the chapter leans on But when her gaze swept around and landed on Jiang Li, who was standing at....
Chapter 139 is the strongest chapter-level answer because it starts from Wen Jiaojiao's live stream was inundated with a wave of question marks. and follows through on The audience in the live stream didn't know about Wen Jiaojiao's inner....
The best chapter pointer here is Chapter 136, "Jiang Li Can Actually Draw Talismans?!". It opens with A few people retraced their steps back to the place they had just been. and closes on Aunt Ying and the camera PD arrived soon after..
Chapter 119 is the strongest chapter-level answer because it starts from What is Princess Wen talking about? and follows through on For some reason, he always felt there was a mysteriously calming power....