Spoilers for Sailor Moon R, the second season of the Sailor Moon anime and the manga chapters attributed to that storyline.
Chibi Usa is a character that fans love to hate in the Sailor Moon fandom. They find her annoying, as her first introduction to the series showed her having massive daddy issues. Since she’s from what is supposed to be a utopian future, this left many fans wondering why.
There are many questions surrounding Chibi Usa's attachment issues, and why she connected so heavily with young Mamoru upon first meeting him. There could be some evidence in the psychological aspects that could have impacted Chibi Usa’s decisions in the second season of Sailor Moon, Sailor Moon R.
In Volume 3 of the manga, Chibi Usa falls from the sky demanding the Legendary Silver Crystal. She seems to know enough about Usagi Tsukino to discern that she carries the artifact. It’s unclear in the anime if she knows it’s her at first. When she falls from the sky she accidentally kisses Mamoru on the mouth. Pushing Usagi out of the way would become a symbol for her character arc in Sailor Moon.
Chibi Usa inserts herself into Usagi’s home and life in a way that was very upsetting for fans. Since the Senshi just defeated Queen Beryl and were trying to live somewhat normal lives, this little girl really threw a kink into things. Later on when it would be revealed that she was Usagi and Mamoru’s daughter from the future it would be even more confusing due to her obvious daddy issues.
From her first introduction, she really connects to Mamoru. She feels warm and safe, even mentioning that he seems “just like Daddy.” The psychology behind her connection with him seems to stem from her being so scared and out of place away from her home in the future in a totally unfamiliar time period. This is an adventure that she's pretty much alone in until she can verbalize what's happening to the Senshi.
It's revealed through glimpses into the future that the perception she had of her parents and the other guardians was that of a lonely child. She was left to be on her own for long periods of time because her parents Neo Queen Serenity and King Endymion were running an empire. The times that stick out the most to her are when her father would read to her at night, and when he would spend time with her outside his work. As a child who longingly wishes to be near her father, it would make absolute sense that she would want to be near a father figure like Mamoru.
Later in the series, when Chibi Usa is turned into Black Lady by the Black Moon clan they used her massive insecurities to turn her into a villain when really they were innocent fears any little girl might have. Her want for Tuxedo Mask's attention as an adult would imply that she still has abandonment issues when it comes to men.
Seeing as Mamoru was the only significant man in her life in the future, the problem would stem from there. Her emotional age is also shown during her embrace of her beloved Luna-P doll, hinting at the fact that she is still very young mentally.
At the time she had to go back into the past she was only 5 years old in human years, or 900 in Crystal Tokyo years. Still very young and still very impressionable. By watching her parents interact with each other and not having many other examples of what an adult relationship looks like she most likely assumed that kissing was an expression of love. At that young age having been alone for so long, she probably didn’t have any other real experience with it. In the future her parents are very busy, so even the basic things like giving hugs or praise would have been few and far between.
After the battle with the Black Moon kingdom she seems to have healed most of her insecurities about not being close enough with her father and future family. As they move on into the third and fourth seasons she is much more mature. She goes on to create healthy relationships with others which tells audiences that her infatuation with her father, like most other kids who experience the same circumstances, was fleeting. Fans get to see more development as her role changes to that of Sailor Chibi Moon in future seasons.
In other words, it was just a phase that needed to be addressed and worked through. Thanks to the help of the Senshi and her parents in both the past and future, she was able to overcome that feeling of yearning. It was never something that was meant to be overtly sexual, she never wanted him in that way.
She only wanted Mamoru to show her the kind of attention she saw him give to her mother, because she was jealous that they spent so much time together. She thought if she could give him that as well, maybe he’d spend more time with her.