Men prefer morally virtuous women.
This is the Spear Counterpart to Single Woman Seeks Good Man and the more or less adult version of All Guys Want Cheerleaders and All Guys Want Sorority Women. When it comes to purely sexual attraction, guys prefer hot and sexy women with a certain raunchiness to them. Just like girls turned-on by bad boys. But when it comes to potential wife material, most men agree on preferring a woman who is just as beautiful on the outside as she is on the inside, the "wife"-type in The Three Faces of Eve and Betty of Betty and Veronica. Which is why men looking for a serious relationships believe in My Girl Is Not a Slut and favour girls who would say "I Will Wait for You". Usually, the guy with this mindset, not unlike his female counterpart, has already had one or several unsatisfying relationships which were more based on the physical level, and is now a mature man (more often than not in his 30's) who wants to settle down and raise a family. But you can't raise a family with a vapid skank with no brains, unless said vapid skank is meant to die at one point. So it only comes naturally that such men prefer women who they can actually rely on to raise their kids and be a good mother. Alternatively, if the family isn't part of the equation, maybe the guy is tired of dating villainesses and would now rather have a relationship with a girl whose morality he may not have to worry about. Or he actually like his villainess girlfriend, but would rather have her clean her act before going anywhere serious. More rarely a First Love but it can happen, double points if the girl is a virgin. Important note: Guys who court women only for their beauty don't apply here. They only apply if they choose the girl also because her personality attracts them and if they actually want to commit in a way or another. If they go after her because she's beautiful but nothing else or just for a nooky session, it's not this trope. Sister Trope to My Girl Is Not a Slut. Contrast Dating Catwoman. Compare All Girls Want Bad Boys and Single Woman Seeks Good Man.
Examples:Anime & Manga