It is mostly episodic. Most cases are covered in single chapters. Some cases take a few chapters to finish. It uses a very satisfying formula: Revenge against the scums/evil. Terrible people get what they deserve. The scenarios are interesting because they are very much based on real issues. You can imagine something like that happening for real. Shady credit card scam, out-of-control teenager crime (they only gets sent to juvie), identity theft, bullying, plain old lie, etc. Some of them are based on international situations such as anti-japan education in China (well, this manga is old. it is mostly gone now), and US military bases in Okinawa. So if you are sensitive to these issues, maybe skip this one.
Characters: the manga starts with the main heroine only, the main owner of the revenge shop. The way this manga adds new characters is a bit different. New characters start out as minor characters who show up once in a while. They show up more and more often and eventually become regular. That includes the information guy, the otaku, the male prostitute (heroine’s younger brother), the high school girl, and the shady doctor. They all end up working under the heroine. The police are there (of course). Some clients come back for more cases. Some villains also come back. There is a final boss too, the cult organization. There is also a branch office in Okinawa too.
Story development: Being episodic does not mean there is no story development. Throughout the manga, the heroine is only referred to as the revenge shop. Her real name, age, and past are mysterious and rarely mentioned, but you can tell her past is related to the main recurring villain of the manga, the cult organization (which actually functions by scamming people). Many chapters are building toward the final fight against the cult, particularly the cult leader. The heroine is clearly preparing for something. Everything is resolved in the last volume.
Character development: Rather than actual character development, it is more like you know more and more about the characters:
At the beginning, the main heroine seems cold blooded and only cares about money. She does not help without an order from the client plus a big sum of money. She is very manipulative and would not hesitate to exploit the situation (and the target) to earn big time.
Later on, it is shown that she refuses to help without being paid because she knows what she does is not justice in any sense and doesn't want to make herself feel that way. And we get to see more and more of her "kind" side. She usually hides her kindness behind some kind of "selfish" motive: she urges the information guy to quit smoking supposedly because she does not want to lose an excellent information agent. She saves the high school girl from her rapist stepdad as a loan to get the high school girl in her team. She helps a disfigured woman revenge in exchange for acting as her double when necessary (the heroine pays for the plastic surgery). ETC.
She also has an eye for people’s hidden potential: the otaku’s imagination and athletic family background, the high school girl’s plain jane existence and the ability to objectively analyze herself.
Other characters also show more and more of who they are:
The information guy is known to be a tech genie from early on. He is later shown to have a very strong sense of justice and would pay to save people he cares about without taking any credit (one time he even gets mistaken as the bad guy by the person he saves, and he just quietly walks away). He is actually also the only character who permanently changes his look throughout the series (except for plastic surgery people), shorter hair and contact lens (and not dirty anymore; he is originally quite dirty).
The otaku guy starts out weird and a little creepy. Later on, his athletic setting and creative mind give him lots of cool moments. He also grows more confident of himself and gets quite royal to the heroine as she is the only one who appreciates him for who he is.
The high school girl gets more confident in herself and becomes more useful (sad). The handsome host is just the handsome host (he is a regular but I can't quite catch his character traits). The doctor is always creepy.
