TWilight refrAIN

TWilight refrAIN is a vertically-scrolling doujin shooter by Eikyu Loop released at Comiket 74 for Windows PC. Players take the role of one of three pairs of characters, one character being present during a given time but they can swap places with each other, and weave through a series danmaku across multiple stages. Each duo has a "Balanced," "Attack," and "Defense" styles that affect their attack power and their ability to use special attacks. The game also features branching paths at certain points of the game that can affect the outcome of the story.

A fan-made English patch by Tenka Seiha can be downloaded here (requires v2.00).

See also Twilight Insanity, this game's predecessor, and Alternative Sphere, a prequel to the series.

Tropes used in TWilight refrAIN include:

Always Identical Twins: Ririka (older sister) and Rurika Mikahashi (younger sister).
Bullet Hell
Dude Looks Like a Lady: Narumi Kirishima, due to his effeminate appearance.
Fan Translation
Half-Identical Twins: Narumi (older brother) and Mizuki (younger sister) Kirishima are fraternal twins.
More Dakka
Multiple Endings
Shoot'Em Up