The weapon wielded by [[reisen (touhou bougetsushou)|Reisen II]] in the infamous [[Koishi Komeiji's Heart-Throbbing Adventure]] fan series.
Its appearance is (generally) that of a very large, black, white highlighted, futuristic [[sniper rifle]]. (It is indeed quite a large weapon, especially for Reisen's small stature, who is almost dwarfed by it and she has to put the stock under her arm in order to use the scope. Though, she never seems to explicitly find it unwieldy or otherwise struggle with it.)
It doesn't use conventional bullets or any apparent projectiles and has no official explanation of how it works. Still, given its name and how it is seen operating, it is speculated it somehow manipulates spacetime to deliver its "payload" instantaneously to the target, [spoiler]to quote Reisen: "You can't dodge a bullet that's already hit" (bullet being likely metaphorical)[/spoiler].
Because of its unique appearance, ability, and infamy of its source material (and maybe a bit of "rule of cool"), it has become [i]somewhat[/i] popular in niche reference media.

[spoiler]It was first seen when Reisen II engages [[Yakumo Yukari]] to assassinate her. Although the first shot doesn't impede or even phase her, its unique ability is first demonstrated and it seemed to have completely erased her midsection from existence without any apparent sign of it firing, thus even without its special ability, it is still extremely deadly. This seems to change Yukari's tactics as she forces Reisen into a close-quarter engagement to negate its range advantage.[/spoiler]
[spoiler]Its second and final appearance is when Reisen II attempts to assassinate [[Hakurei Reimu]] next, who was in the middle of fighting [[Koakuma]]. Fortunately for her, this assassination is foiled by [[Reisen Udongein Inaba]]. Interestingly, Reimu appears shocked at the sight of the weapon and recognizes it by name, implying some further significance, which is unfortunately never explained.[/spoiler]
time warp rifle