First Meeting
How exactly did Chibiusa and Hotaru first meet? Well, both involve Chibiusa's hat, but there are some differences in respect to the anime and manga. I have both listed below.Anime
Earlier in the episode (titled Shin no kyuuseishu ha dare? Hikari to kage no chaos Who is the Real Messiah? Light and Shadow in Chaos), Chibusa had begged to go to the park with Usagi, Ami, Minako, Makoto, and Rei because Setsuna was already gone. The girls were relectant to go, because they were busy trying to figure out the location of the Messiah, but once Chibiusa mentioned the name of the park (Juuban Shizenkouen) Minako was estatic to comply with the young girl's wishes. The other girls weren't fools, and Ami bluntly questioned Minako on why she would want to visit that particular park. After a quick moment of Minako playing dumb, she confessed that the park was being used as a shooting place for a movie staring a famous actor, Eda Yousaku. The girls one by one agreed it would be okay to visit the park for a change of pace.
Once at the park, the girls find the shooting spot, and enjoy themselves. Chibiusa, being shorter than the rest of the crowd, has to repeatedly jump up and down in hopes of catching a glimpse of the action. A strong gust of wind blows suddenly, and steals Chibiusa's hat right off her head. The young girl is chasing after her beloved hat, because it was a present from Usagi's mother. Chibiusa's yelling distracts a young girl, dressed in all black, from her book. The young girl follows the floating hat with her eyes, then puts her book down on the bench, and joins in the chase for the run-away hat. The object lands a few feet from the river, and the young girl lands right on top of it, so it won't float into the river. Chibiusa eventually catches up, and is very glad to see her hat has been caught. The young girl gives Chibiusa her hat back, commenting on how she's glad it didn't end up in the river. A sudden attack takes over the girl, and Chibiusa asks if she's okay. The girl reassures the pink-haired girl that she will be; the attack just needs some time to pass. After a few moments, the girl is okay. Chibiusa still seems a bit worried, but shakes it off with a smile. She asks her hat savior if she would like to play, much to the girl's surprise. Chibiusa introduces herself with a smile, and the young girl follows her example, saying her name is Hotaru. The animators stressed the importance of this scence, with once the two girls join hands, a beautiful background surrounds the two, and the animation is softer. There is a close up of Chibiusa's and Hotaru's smiling faces, then a pan out of the two happy girls from above.
Manga
In Volume 7, (Chapter 24) Chibiusa and her friends are at an amusment park, being chaperoned by Mamoru and Asanuma. Momoko and Chibiusa ride a rollercoaster, during which Chibiusa's har flies off her head due to the high speed. When the ride is over, Chibiusa get off and goes to find her lost hat. Momoko rejoins the group, but Mamoru notices Chibiusa is absent, so he goes in search of his future daughter.
After some searching, Chibiusa luckily finds her lost hat. She looks up, and sees a girl crouching on the ground in pain. Chibiusa approaches the girl, hoping she can somehow help her, but the girl pushes her away, saying the area is off limits to outsiders. While trying to find her friends, Usagi runs into Chibiusa. She asks what she's doing here, and Chibiusa explains how she lost her hat, and found his girl in pain. Before Usagi can do anything, a daimon monster appears from behind the corner. The two senshi quickly transform.
Chibimoon blocks the innocent girl from the monster, but gets bitten on the arm. Sailormoon calls out in horror, and prepares her "Moon Spiral Heart Attack". The attack lands its mark, and frees a cat from the being posessing it. When Hotaru gains control of herself, she questions who the two senshi are. Chibimoon takes the lead, and explains they are Sailor Senshi, and asks if Hotaru is hurt. Hotaru glances up, and tells Chibimoon that she is the one who is injured. The young senshi realizes she has been bitten, so Hotaru takes the soldier's injured arm into her hands. Meanwhile, Sailormoon senses someone watching them, and turns her head quickly. She catches, along with Mamoru and the other girls, a glimpse of a mysterious senshi and a Tuxedo Kamen imposter. Before Sailormoon can fully understand what she's seeing, Chibimoon calls out that her injury has been healed. Sailormoon is shocked, while Hotaru tells Chibimoon to disinfect it when she gets home. She comments that it's odd to have these healing powers, and she's had them ever since she was a small child. Mamoru calls out to his future wife and daughter. Hotaru warns her protectors that they should be on their way, because if the guards of the property finds them, they will be in trouble. Chibimoon thanks the girl for the warning, then asks if she could tell her her name. The young smiles, and introduces herself as Tomoe Hotaru before entering the research building. Chibimoon quietly says, "Hotaru-chan" as she watches the girl until she's out of sight.