Funnily enough, her gun is almost definitely grown too. In the image used as the example for Shuro on Danbooru (post #6941490), her gun covers more of her overall height than the gun in this image, but is also on a steeper angle. Eyeballing it (since I can't measure directly or anything), it looks like the overall height covered by both guns to their respective Shuro would be about the same if their angles and position were the same.
Pretty cool ngl. Whatever method Shuro used for this, it's clearly better than Saya potions, since as far as I recall Shun's sniper didn't get any smaller.
Maybe a Super Mushroom or something? That usually makes Mario/Luigi/whoever's clothes grow too, so why not a gun?
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