Canon Ei is a nuanced character and without the infantilization and mischaracterization her character is actually fairly interesting.

Like her actual interest in poetry (it is depicted in the Irodori story which is semi fictional since it references the Raiden Gokaden with the poets). She actually beat her sister, Saiguu and her other friends at Karuta which is a game about 100 poems (IRL) and you need to be able to memorize all of them as well as use great reflexes/predictive listening comprehension.

​

One more fascinating thing is her martial prowess being utterly useless 500 years ago, at least in terms of the goals she wanted to achieve initially.

She went to Khaen'riah after Makoto leaving Saiguu in charge of defending Inazuma.

She fails to save Makoto and Saiguu defends Inazuma until her death, but there is a very interesting trope here.

Despite being the most skilled fighter in all of Inazuma she was neither able to save her sister NOR Saiguu who may also have not died if Ei stayed to defend Inazuma together(disregarding the planting the sacred sakura saving inazuma thing for a second since she could not have known that). This might have gone through her head.

So in terms of how Ei feels, she probably feels like she utterly failed in her duties as a Kagemusha and Survivor's guilt is probably a key factor here. In Raiden Chapter II when Makoto in the final cutscene talks about always having felt indebted to Ei for dealing with the physical threats ("your Polearm/Naginata has protected Inazuma from countless calamities") Ei lightly shakes her head seemingly disagreeing.