One of the functions of being a published writer is the ability to meet deadlines. Deadlines mean that you don’t have the luxury of running dry or writing when ‘inspired’. You will have to be aware of your writing process and conceptualize your idea with an eye to generating an endless series of plots and characters.
It’s interesting that the best way for endless character generation involves not thinking out of the box, but tying your creativity into box...a creative limit. Think of poetry; the Japanese Haiku or a Sonnet both involve creating beautiful works of art within strict boundaries. Yet the endless variety of poetry that has evolved from within these boundaries are breath-taking. You can say the same about a human being; there are certain features that a human being comes with: two arms and legs; a head, two eyes and one mouth. Yet you can’t say that there’s one human being that is alike.
So it is with creating endless characters. Give your characters in your story a theme to draw from and you’ll suddenly have endless character variations on a theme. I’ll look at Fruits Baskets to illustrate the point.
Fruits Basket's characters are based on the Chinese Zodiac and the 12 animals that represent the Zodiac. The premise of Fruits Baskets is this: Tohru Honda is an orphaned student who comes to live as a housekeeper in the family of one of the boys in her highschool. She finds out that the family is under a curse which changes them into a animal of the Zodiac when hugged by the opposite sex. As time goes on and the tragedy of this situation unfolds, she becomes determined to free the family of the curse.
In the set up above, the number of characters that the author Natsuki Takaya can introduce which are relevant to the storyline is finite. However, those 12 Zodiac characters translated to 23 volumes of manga. If you're lucky to have a series that runs that long, that's more than enough. Each character would have their own story arcs woven into larger story.
1. The Cat
2. The Mouse
3. The Dog
4. The Ox
5. The Pig
6. The Rabbit
7. The Snake
8. The Tiger
9. The Dragon
10. The Monkey
11. The Horse
12. The Rooster
Other examples in creating characters on a theme are:
1. Full Metal Alchemist's Seven Deadly Sins
2. Utena has different colour roses for the Student Council
3. Sailor Moon's sailor scouts are named after the planets in our galaxy and the villains named after precious stones