That's Houshou Marine, and the original image is art by AkasaAi.
Requires login: https://x.com/akasaai/status/1734176055030895075
But of course we have the Boorus to bypass that.
https://gelbooru.com/index.php?page=post&s=view&id=9343329
https://gelbooru.com/index.php?page=post&s=view&id=9346179
That's Modernia, from Nikke!
Seems the source for this one is kind of elusive. That's the official Nikke MMD model for Modernia, but the specific fan-made video escapes me.
Seems the only reliable sources are Reddit threads.
https://www.reddit.com/r/GIRLSundPANZER/comments/195r93q/i_finally_have_them_all/
https://www.reddit.com/r/GIRLSundPANZER/comments/o3yd8r/girls_und_panzer_characters_but_kfc/
As it turns out, this is a completely original character. Imageboard sites don't have it tagged as being any particular character.
For your reference (as always, NSFW warning):
https://danbooru.donmai.us/posts/11033912
https://gelbooru.com/index.php?page=post&s=view&id=13732995
Just to throw in a little detail, this Polka is from Eternal Sonata, a videogame. You can find the ACDB entries for the game and the character at the top.
Why that's one of my heroes! That's Tatsuya Suou, one of the two protagonists of the Persona 2 duology. That specific image is official art of his appearance in Eternal Punishment - the second part of P2.
Here's a link to it: https://megamitensei.fandom.com/wiki/Tatsuya_Suou/Gallery?file=TatsuyaIcon.png