[LightElf]

When writing a story, there are basically 5 general steps to consider. Below is the first one.

1. Brainstorming --- You make up a story (under the assumption that you're writing a short story of course. I assume this is not a long-thread novel project?), think of the exposition, climax/es (or turning point or whatever), and conclusion. During the exposition steps, the main characters are usually introduced (you can bend this rule a bit, depending from story to story). But it is important for you to realize that a story, like the base of a tall tower or something, must have a clear cut good exposition to support it well. But not all stories are the same.

Different stories need different ways of approaching when using methods of characterization or other literary devices to develop character. In other words, whilst it may be possible to write a story based on the initial personality traits of the characters, it makes much more sense, and gives the story more originality when the characters accustom themselves onto the story, not the other way round (so the story should shape the characters, not vice versa).

So as someone posted earlier, yes, some nerdy girls may be cold and distant and likes facts, whilst the artistic one may be more open and socially outgoing. These are some typical, maybe even clichee to some extent characteristics of nerdy and artistic characters used in many mangas. You may well start there and further develop your characters if your story complements it well (like Motoko's development from a cold and distant kendo fighter to a more open and sociable character later in Love Hina). Or you may let them continue having the same characteristics, again, should your storyline complement it well.

But this should not always be the case. Again, depending on how you wish to unfold your story, you may even decide to give the artistic girl rather the cold and distant personality traits, perhaps because she grew up in a secluded environment and has therefore become a rather less sociable character who prefers to spend her time observing nature and other things to transfer them into art, through which she wants to fight back her loneliness, get recognized by others, and become the popular mangaka you mentioned. The nerdy girl on the other hand may be a super-smart girl who is not cold and distant, but rather very outgoing and altruistic, using her intelligence to support others, or maybe even be a rather supercilious girl who only hangs around with other people "on her league" and lectures "lower" ones with high vocabulary and mocking scientific language.

You could then further develop these characters personalities to weave into your harem storyline. Harem stories very often include girls of very different personalities and backgrounds, who then later gradually develop their love for the guy in question.

so you should not hold onto some Psychology "principles" to better get to know a typical female character, but rather let your storyline fluidly shape your characters to add depth and originality. hope this was useful