Sunny has always hung around Luna and Star for as long as she could remember and for a fairy it isn't likely she can remember that far back. All the fairy of light needs to know is she is the leader type of what everyone dubs them as 'Three Mischievous Fairies' which isn't that far off. Sunny is always planning a prank against humans, mostly against Marisa and Reimu. Sunny's favorite thing it to help them get lost, always trying to mislead them into a fowl but very amusing folly. Though there are times when the three are caught during their prank, or in this case it's usually Sunny and Luna as Star seems to always have a bit more awareness due to her ability of detecting moving noise. In most cases, they're caught by either Red-white (Reimu) or Black (Marisa).
They met with Cirno along the way, deeply impressed with her ability to win at Hide n' Seek as well as her usage of the ice powers. The three become good friends with the ice fairy, playing with her off and on between pranks and drinking the seasons away. They also met with Daiyousei once, but had no opinion about such a passive fairy. Dai-Chan was very kind and shy though, so they may have to invite her over for a few drinks.
Sunny one day decided to cause an incident. Why did the fairy decide this? Over some sake they stole, the three were discussing about different incidents after they hired Marisa to help get their tree back from the Vine Youkai. It was short and sweet, as the Vine Youkai was preventing them for getting into the tree they once lived in. So they went to Marisa for help. Sadly, Marisa was useless as she couldn't use her Master Spark as that would also destroy their home, thus causing the Vine Youkai to leave on its own accord after eating everything in their home.
Now the three fairies were talking about how different Youkai caused an incident that caused Reimu and Marisa to put a stop to it. They went through mentioning the Scarlet Mansion, the endless winter, the night that would not end though that was Luna's favorite. This went on and on until the new year in which Sunny had a dream. It was the Great Fairy War in which all the fairies would attack the human village, even drew out a plan from her dream that would be incident worthy. Then she thought she could enlist Cirno's help, by destroying her home. However she was busy so they left a flag for her to find. Later that day they found a note that said someone was declaring war, without a name. They we're excited and started gathering fairies, but it weren't until spring that Cirno remember and went out to attack the three. In the end, the three lost but remained friends with the ice fairy and the human's were safe from something other than the usual pranks.
Not too long after, a giant tree was struck by lightning behind the Hakurei Shrine, damaging it heavily. Reimu tries to make it an attraction but the fairies had other plans. Using their powers combined then gave new life into the tree and decided to make it their new summer home. However, someone happened as the three was back to its normal self within a few weeks. But the fairies decided to move in anyways only to be confronted by Yukari, the Boundary Youkai. She tested them in a Danmaku fight and lost horribly due to it. The test was to make sure that they weren't strong enough as the tree itself was caught in the field that separated the outside world and Gensokyo. However, after calling them too weak she allowed them to move into the tree with no worries. Sunny was thrown off but it seems Star was happy and cheery about it like usual; not helping that it was more insulting than flattering.
The fairy of bending light usually takes charge when it comes to planning and plotting pranks the trio do together. Oddly enough she does put a bit of detail into her plans, including Luna's power to mute sound around them and Star's ability to detect moving objects at a distance. The three use their powers often to support each other and usually highly succeed. While most of the time she argues with Luna due to the fact she gets in the most trouble when it comes to getting caught, though it's always Star first to leave the scene of the crime. Sunny takes the Leadership role with her plans and very forward attitude, though he often runs away at the first sight of trouble or when a human is in sight. She also has a weakness for delicious food and loves alcohol as much as the next Oni.
Sunny has light blue eyes and short gold hair braided by the sides of her head and a maid like white headband. She wears a dress-like cloth which is red and white colored, decorated skillfully in ribbons just below both her shoulders and a large yellow ribbon that ties around her collar. Another one of her outfits happens to be one of the maid outfits from the Scarlet manor when her, Star and Luna snuck in during the rainy reason and pretended to be a pair of the staff just to pass the time until the rainy season ended. Good thing they weren't caught. She has a pair of wings that apparently isn't directly connected to her actual body.