I read a lot of theories about Tsumugi and Kaede having some kind of connection, combined with the assumption that Kaede has a twin. Also there could be a parallel with Junko killing her sister (Mukuro) in an unjustified way and Tsumugi leading Kaede to be executed.

I decided to compare their sprites and woah.

The King of Fighters '98: Unused Sprites

To the left, an unused standing animation for Kyo Kusanagi found within KOF 98's debug menu. The Cutting Room Floor speculates that this unused asset was intended for Kyo's second playable form, the one based upon his KOF 95 appearance.

For KOF 98's final release, both versions of Kyo would end up using the same stance, which can be seen up above, next to the unused one.

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Metal Gear 2 Solid Snake: Codec Portraits

In 2004, Konami would update and re-release the first two entries in the franchise, Metal Gear and Metal Gear 2∶ Solid Snake for mobile phones. The updated versions would later be available on the PS2 as bonus games in Metal Gear Solid 3∶ Subsistence, as standalone titles in the Japanese WiiWare store, and current generation platforms via The Metal Gear Solid∶ Master Collection.

Whereas both re-releases received general quality of life improvements, only Metal Gear 2 received significant visual changes. The primary reason why Metal Gear 2 needed a reworking is the unauthorized usage of various celebrity likenesses.

In the original release, Snake's appearance is based on Mel Gibson, Big Boss clearly uses Sean Connery’s likeness, Dr. Madnar is essentially Albert Einstein and Colonel Campbell looks almost identical to Richard Crenna in First Blood.

Interestingly enough, the character portraits used for the codec conversations are clearly based on the ones from Metal Gear∶ Ghost Babel. At first glance, some of the sprites appear to be identical.

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Pretty Soldier Sailor Moon: Unused Sailor V Sprites

User Roket at The Spriter's Resource discovered these unused Sailor V sprites from Pretty Gaurdian Sailor Moon, an arcade adaptation of an anime adaptation of Naoko Takeuchi's iconic magical girl manga.

Since they're both identities of Minako Aino, it makes sense that these Sailor V sprites use Sailor Venus sprites as a base.

This compilation of unused dialogue portraits includes a few of Minako's Sailor V persona. Interestingly, two of the portraits have a color scheme similar to when Zoisite imitated Sailor Moon in the anime's first season.

That disguised version of Zoisite actually appeared as a palette swapped boss in the SNES adaption of the anime.

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Capcom Fighting Evolution: Updated Sprites

Unlike most others, this Capcom fighter isn't fondly remembered for its visuals. Instead it's thought of as essentially being a M.U.G.E.N. game, except this is no fan project.

Aside from Ingrid, none of the other playable characters in CFE use wholly original sprites. At first glance, Demitri, Guy and Zangief’s sprites appear to be ripped directly from their appearances in Darkstalkers, Street Fighter Alpha and Street Fighter Alpha 2, respectively.

But upon closer inspection, you'll notice that Street Fighter's Russian wrestler and the streetwise shinobi look slightly different. Guy's updated idle stance maintains the previous version's cool composure.

Conversely, Zangiefs' sprites from the Alpha 2 were modified to look more animated, blowing steam from his nose like a cartoon bull.

As you can see, these new sprites rework the proportions of their characters, and this is most apparent when looking at Demitri's idle animation.

Super Mario Maker Series: New Old School Sprites

Released in 2015, Super Mario Maker was the first mainline Mario game in 20 years to use sprite based graphics.

The main concept of Mario Maker is that it’s a sandbox for players to design their own Mario stages to play and share with others. Creators are able to render their stages in the style of four classic titles∶ Super Mario Bros, Super Mario Bros 3, Super Mario World and New Super Mario Bros U.

As everyone knows, those first three games used 2D pixel art, which necessitated the developers of Mario Maker to create new sprites in the style of those games.

In the original release of Mario World, Bowser looks like this when you fight him at the end of the game--

But when you create a SMW style stage with King Koopa as an enemy, he looks radically different. Notably, Bowser can now fight independent of his Clown Car.

If you're creating a stage styled like the classic Super Mario Bros, you can now include two new power-ups not seen in the original version∶ Weird Mushrooms and Mystery Mushrooms.

The Weird Mushroom transforms Mario into a tall, slender version of himself. Gameplay-wise, Weird Mario plays similarly to Luigi in Super Mario Bros 2.

Mystery Mushrooms transform Mario into "Costume Mario", giving him a different outfit, or the appearance of one of his co-stars, other Nintendo all-stars and third-party characters like Hello Kitty.

Some of the costume sprites are wholly original or reuse ones from older game. Some of recycled sprites are altered in some way for the purposes of this game.

It's also worth noting that these costume sprites don't follow the same three color limit that an actual NES sprite would.

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World Heroes 2 Jet / The King of Fighters '97: Zeus & Orochi Yashiro

Zeus' intro/taunt animation and Orochi Yashiro's standing animation look pretty similar and after making a few modification to them, they look even more alike.

For this comparison, I removed a few frames from Zeus's stance and reversed the animation on Orochi Yashiro's. You’re getting sleepy… ᶻ 𝗓 𐰁