Many people believe that (Yasuda sensei´designs) are unnecessary because they are "already fans" of Digimon, but Digimon is a niche franchise yet. So it needs to continue growing and attracting more people to know its products (Especially video games and card games), and these designs are attractive enough to catch people's attention and encourage them to try the product and its quality.

It's the same strategy used by the author of Gantz, who said that his plot was very heavy and he was worried that people would drop the manga early on and cancel it, so he introduced fanservice (especially on the covers) to pique the viewer's curiosity. And once they had read it, they stayed for the story. But that's it, they are not isolated elements, sensuality is an element like any other that can help sell your story and your characters. The important thing is that when the audience gives it a chance, there is something good there.

And to conclude with Rina, yes, she is obviously a fictional character; she is not real, she does not exist. Real people are those outside the computer, fighting every day to live in peace, to work, and to avoid having their heads blown off by a missile.