She's a slender, cloaked woman wielding an oversized weapon.
There have been plenty of slender women who wield oversized weapons. Just off the top of my head, Meru from Legend of Dragoon, Ryuko from Kill La Kill.
Hell, plenty of slender men wield oversized weapons as well. See: Cloud Strife, Sephiroth, Zabuza Momochi...
** It's a common trope. ** Nobody is copying anyone.
Her weapon is a giant rectangle with a hole poked through the middle of it, but this time it's a gun instead of a sword.
Using that logic, Transistor is a rip off of Xenoblade.
The Monado is a sword with a hole in it, ergo Transistor is a copy, right?
The weapon absorbs the souls of the things it kills to empower itself.
...and?
There's a whole reason for her weapon doing that. The Thresh/Lucian/Senna storyline (which, btw, came out in 2013, one year before Transistor's release) has revolved around souls and killing or saving them.
But because Transistor was released in the meantime, that means Senna is now copying Red's design?
Senna can become a wraith and traverses a spirit realm similar to Transistor's alternate digital realm.
1 - Senna doesn't "traverse the spirit realm", she just camouflages herself as a spirit. Nowhere in her base lore (unless I missed something in one of the side stories) does it mention her going to the realm of the spirits, just that she covers herself in the Black Mist.
2 - Even if Senna did that, Red wasn't the first person to traverse a spirit realm. Shen currently does it, Lilith from Borderlands does it, plenty of other characters have done it before her.
She has narrative about her and a loved one combating evil captors.
Yeah...? The theme of revenge is massive if you know... writing lol
The evil corrupting the Shadow Isles is quite similar in concept to the Process corrupting the Cloudbank, in that they're plagues that resurrect the dead and change the scenery and somesuch.
And the Shadow Isles were released in 2013 or before then, a year before Transistor's release, so what are you getting at?
Really, the only differences I see are the color pallet and the sort of game they're in.
Yes, let's ignore the story and setting of each character (Transistor's futuristic setting to Runeterra's more medieval/fantasy one), their fighting styles (Red's close combat sword style compared to Senna's ranged, supportive one), and the context of why they do what they do, instead choosing to call it all a rip off.
Even though, for the final time, Transistor came out after Thresh/Lucian and basically everything about Senna was designed/created/conceived at that point in time and has roots linking back to the originals created in 2013. Come on, man.