So do your best to find an alternative to "boring" and "obnoxious" characters.You should ask questions such as, "Why would anyone like this person?Perhaps you are interested in creating a cute story in which the main character can end up with one of several love interests.
You can create a love story in which a single sex scene is an important landmark for the characters.
Or you can create a game filled with challenges and/or puzzles, and make it difficult to get to a sex scene.
Stereotypes: some character lists in bishoujo and otome games can seem like checklists of fan-favorite character types.
(Patient Childhood Love Interest, Meido, Ojou Sheltered Aristocrat, Not Blood Siblings, Troubled, but Cute, Token Mini-Moe...) Add some unique-but-not-bland characters, or at least add some variety.
However, there is reason why Dating Sim use this character less and less.
Mary Sue: if your main character is female, some fans may be quick to label her a Mary Sue, or as some sort of stand-in for Fangirls. Just show the audience that she has plausible strengths and real weaknesses.
Likewise, many commercial games have a Slice of Life setting.
If your setting is realistic, then make sure you can portray it in a way that the audience will find interesting.
Therefore, you need to devise interesting ways for their feelings to develop. If your game will have one, then find a way to make it logical.
Note that harems do not necessarily exist in doujin visual novels.
If you have decided to create an adult game, then you need to decide how sex will be incorporated into the story or the gameplay.