I think one of the most noticeable differences is that mangakas often work with a group of assistants, while comic artists do most of their work by themselves (some comic artists might have assistants, but in general the workflow is not as structured).
Here is a team of five assistants gets to work on a manga drawn by Kumagai Kyoko (shown in the back of the picture).
Most mangaka have assistants who help them complete their work in a clean and timely manner. The duties of assistants vary widely, as the term incorporates all people working for a mangaka's art studio, but is most commonly used to refer to secondary artists. The number of assistant artists also varies widely between mangaka, but is typically at least three. Other mangaka instead form collaborative groups known as "circles" but do not use additional assistants, such as the creative team CLAMP. A few mangaka have no assistants at all, and prefer to do everything themselves, but this is considered exceptional.
Assistants are commonly used for inking, lettering, andshading, though the predominance of black and white art in manga means that unlike in the western comic industry, a studio rarely employs a colorist.
Some mangaka only do the sketchwork for their art, and have their numerous assistants fill in all of the details, but it is more common for assistants to deal with background and cameo art, leaving the mangaka to focus on drawing and inking the characters. Assistants may also be employed to perform specialized artistic tasks. Go Nagai, for instance, at one time employed a specialist to draw helicopters and other military vehicles.
The second point is that the unique editorial system in Japan dictates thatmangakas need to have a very close, strong relationship with their dedicated editor.
One reason often given for the high quality of Japanese manga is the prominent role played by the editor. The first stage in the serialization of any manga starts with the artist and editor sitting down together to confer on a story. The artist then draws up a rough storyboard called the “name.” At this stage, the manga is just a crude sketch featuring simple drawings with dialogue. Once the editor gives this draft the go-ahead, work gets started on the real thing. This is the stage when decisions need to be taken on plot and characters development. Depending on the type of manga, the artist may carry out research interviews at this stage. If the artist gets stuck, the editor is the perfect person to provide advice. Many manga works have been lifted to a higher level by a touch of timely advice from the editor. From the artist’s point of view, the editor is a creative partner and close friend, sharing the artist’s anxieties and making sure that work proceeds smoothly. It has been said that the editor contributes around 30 percent of what makes a manga successful.