I'd suggest looking on dedicated manga apps such as Manga Plus or Crunchyroll Manga. They often have a wide range of titles available, including Chained Soldier.
It's hard to pinpoint exactly. The ending point can vary depending on how the anime adaptation was structured compared to the manga's original storyline.
It depends on how the manga is written. If the author creates a compelling world and plot around it, then it has a chance of being seen as a successful profession. But it also needs to make sense within the context of the manga's universe.
The story shows the difficult life of a slave mother in the morning. She might have to deal with tough tasks, limited freedom, and maybe even the cruelty of her masters.
I'm not sure specifically as I haven't read that exact fanfic. But generally, it could be about a character who is in some sort of difficult or entrapping situation related to a 'whirlpool', perhaps in a metaphorical or literal sense.