(Finally! An Ask about Miraculous Juuni!)
Eiji actually started crushing on Kanade when he saw her during a judo tournament before they ended up at the same high school) and in the same class). He saw how skilled she was, how passionate she was about her chosen path, and how sweet/friendly she was to her teammates and opponents. Eiji also likes how spunky Kanae can be.
But when Eiji is Ushii, he has to keep his feelings for Kanae under lock-&-key. However; Ushii does see Tora as a younger sister and cares for her as such when they’re heroes. He’s better with weapons than hand-to-hand.
Kanae, on the other hand, doesn’t care much for Kashii Eiji. To her, Eiji is just one of her classmates. But Kanae adores Ushii because he chooses to do the right thing because it’s the right thing to do (and he might have also saved her during an Akuma battle).
When Kanae is Tora, she tries to take the hero work seriously to impress Ushii, and while she’s disappointed that he sees her as a younger sister, she’s glad that she’s being acknowledged in a good way. She’s very good with the hand-to-hand combat stuff.
(hope this answers your question feel free to ask if there’s something that you want to know (no real spoilers though))