A weapon or ability that generates a big beam which vaporizes everything in its path. Bonus point if the rule of cool is involved.
- Zoltraak, Sousou no Frieren : A powerful spell designed by the demon Qual, the Elder Sage of Corruption. It fires a concentrated beam of mana that pierces everything it touches. It was so deadly that humanity spent decades researching it and developping countermeasures, to the point where Zoltraak is now seen as "ordinary offensive magic".
- The Incinerator, Made in Abyss : The main weapon of one of the protagonists, Reg. It is mounted directly into the cyborg's arm and requires charging before firing. The Incinerator is so powerful that it is said it can "rewrite the rules of the Abyss", and we are shown twice in the show that it can do exactly that.
- Gravitational Beam Emitter, Blame! : the main (and only? It's been a while) weapon of Kiri, the protagonist. While it looks like a simple handgun, it actually uses gravitational manipulation technology that has been lost to time to fire its devastating beam. Its power source is its own user, and it comes with a limiter to how much energy it can sap to operate, in order to protect its user.
- USM field projector, The Expanse (book only): the main weapon mounted on a Magnetar class battleship. It fires a beam that "spaghettifies its targets into hyper-accelerated dust". The energy required to operate such weapon should not be possible, but it uses Protomolecule technology to violate entropy and just makes it work. Not everyone is happy when entropy gets violated.
- C'thun's Dark Glare, World of Warcraft: As the final boss of the Temple of Ahn'Qiraj, C'thun has many mechanics that must be properly executed, lest the whole raid dies. During phase 1, C'thun will occasionally fire up a big red laser of death from its eye, which turns 360 degrees and must be avoided.
Honorable mentions that loosely fit this trope:
- Hollow Purple, Jujutsu Kaisen: it's not a beam, but a fast moving sphere of attracting and repelling energies mixed together. It can only be used by Limitless users.
- The Infinity Ray, Invincible: a powerful laser fired from a gun held by the legendary Space Racer, the infinity ray goes on forever, and destroy everything in its path. But when it comes to superweapons in space, size *does* matter.
- Dust Release, Naruto: one of the few *kekei touta*, Dust Release, also known as Particle Style, generates a geometric shape that then annihilates everything within, down to the molecular level. I don't think it fits the trope because one, it's only a beam if the user shapes it that way, and two, it doesn't destroy the more durable materials, such as plot armor.