Sine

Sine is one of the shifters in the current game, and had been one for 3 days before arriving to Vertia.

As a human
Sine stands tall at 5'7 with a healthy pear-shaped body. She has olive skin, green eyes, and curly black hair reaching to the small of her back, gathered in a ponytail. It is parted in the middle and held out of her face by tucking it behind her ears.

Original clothes
The clothing she woke up in includes a knit sweater patterned green and black like a Sigilyph's belly. The sleeves and her pants are black. The wings manifest as a yellow cape split down the middle and striped with red and blue, attached at the front with a large pin that resembles a nazar. Her boots have a slight heel and have a similar coloring and pattern to her cape, being yellow with red and blue stripes around the boot-cuff. The cape, if it isn't taken off, has the tassels tied together in a knot and out of the way.

As a Pokémon
The 'fingers' of Sigilyph's wings and tail are long and slender, with the red stripes being thicker than the blue ones and the blue stripes coloring nearly the whole feather. The Pokémon's main body is small and rotund, more wide than it is tall.

Backstory
Sine was a legendary Pokémon fanatic. Born in Ecruteak City, Johto, Sine had been surrounded by culture and history and imbued with an insatiable sense of curiosity. In her childhood, she thought she saw a huge shining Pokémon flying through the sky and her obsession with mythological Pokémon began. She wasn't even sure if the bird Pokémon really was the legendary Ho-oh from the books, but she refused to think otherwise.

At around 14 years old, Sine moved with her family to the bigger Violet City and was expected to continue her education in the city's academy. Instead, she would often skip class to either go to the library or wander the Ruins of Alph, evading the researchers and native Pokémon to try to solve the mysteries herself. Her adventurous spirit eventually led her to confront her parents and ultimately travel around the region. The purpose of her journey was to grasp at scraps of information about god-like Pokémon who can control the weather or travel in time and to prove that, unlike the civilizations which worshiped them, these Pokémon still roamed the earth.

She concluded that the rest of the puzzle would be in Sinnoh. Before leaving the region for a few years, Sine went back to Violet City to say her goodbyes to her parents and then visit the ruins one last time, despite the warnings that the area was unstable. She was caught in a cave-in and broke her left leg. While she might have survived even with her injuries (as she sent her trusty Pidgeotto to get help), she was nevertheless approached by the shadow because of her feelings of shock and despair. She gave one simple request:

"I wish to see Ho-Oh again."

It's been about three days since she woke up near Vertia, and ever since she discovered her shift partway through day one, Sine has been aggressively testing the limits of her new form by shifting until she is tired, then reverting to rest before repeating the process. She is familiar with how long she can stay as a Sigilyph and how to control her flight, but she is incredibly exhausted and moody from prolonged exertion.

Personality
Sine is independent and impulsive. If she is afraid of anything, she doesn't let it show in front of anyone. She doesn't like asking for help, which ends up in her biting off much more than she can chew and potentially getting herself in heaps of trouble with her disregard for most rules (mostly the rule 'no trespassing'). Stubborn in a sense, Sine is hard to argue with and would rather leave than admit that she's wrong. She thinks actions speak stronger than words, and doesn't like bragging nor saying more than she has to, rendering her an enigma even to some of her friends.

Aster
Aster is a male Omanyte. He has an Impish nature, the ability Swift Swim, and the moves Bubble Beam, Rollout, Protect, and Tickle.

Matilda
Matilda is a female Onix. She has a Brave nature, the ability Sturdy, and the moves Dragon Breath, Smack Down, Dig, and Bind.

Trivia

 * Prior to the game, Sine wore glasses and she can still be seen absently touching the bridge of her nose when she's thinking, as if trying to adjust them.