Official Move Approval III

[Amaterasu]

Super Move T1 - Celestial Brush: Power Slash - 600, Requires Ranged Proficiency, Area Attack Proficiency

Amaterasu uses the magic brush that is at the end of her hair, turning the very world before her into her canvas. She draws a horizontal straight line into the air and/or onto an object or being, saying "kiru" (japanese verb, meaning "cut") as she does. After a brief delay, an invisible sword delivers a huge slash up to ten meters beyond the ink line, on the side opposite of Amaterasu's (thus if Amaterasu stood on the left and drew the line in the middle, the slash would happen on the right). The slash only affects the first opponent (Prime or Secondary) that it hits, assuming that it is delivered in the direction that Amaterasu drew the line in. It may also cut into the environment such as a wall, a tree or a rock, leaving slash marks and possibly even cut them in half, however they will just harmlessly drop to the ground, never hitting Amaterasu's opponents or herself. Why not? Because Omniverse logic ¯\_(ツ)_/¯
For around one second, the kanji 斬 (zan, meaning "beheading", "murder" or "kill") also appears in the air above Amaterasu as the slash happens, this is a cosmetic effect that does not influence the move itself.

The Super Move- This will cost 1200 cause of either targeting many people or just one.

I'll change the bolded parts to bring the move down to 600 then. Hope it works out!
If the fluff about cutting environmental objects is too strong, I'd suggest this alternative (again, only the bolded parts are different):

Amaterasu uses the magic brush that is at the end of her hair, turning the very world before her into her canvas. She draws a horizontal straight line into the air and/or onto an object or being, saying "kiru" (japanese verb, meaning "cut") as she does. After a brief delay, an invisible sword delivers a huge slash up to ten meters beyond the ink line, on the side opposite of Amaterasu's (thus if Amaterasu stood on the left and drew the line in the middle, the slash would happen on the right). The slash only affects the first opponent (Prime or Secondary) that it hits, assuming that it is delivered in the direction that Amaterasu drew the line in. It may also cut into the environment such as a wall, a tree or a rock, leaving slash marks behind but not cutting them in half or creating other effects.
For around one second, the kanji 斬 (zan, meaning "beheading", "murder" or "kill") also appears in the air above Amaterasu as the slash happens, this is a cosmetic effect that does not influence the move itself.