整理 A いろいろな働きをする助詞 教科書 p.58
Multi-function auxiliary words
接続：N／助詞 + こそ
new… main. Emphasize the object, time, or cause.
注意 / Note：Check the correct front form, subject and level of politeness; Don't just translate word for word.
比較 / Compare：Compare with structures in the same lesson to choose according to function in the whole sentence. Same 課: 〜でも／〜も／〜さえ／〜まで／〜くらい／〜ぐらい／〜など／〜なんか／〜だけ — these models are often mistaken for each other, read the 接続 line carefully and then decide.
今年こそ合格したいです。
This year I want to pass.
こちらこそ、ありがとうございます。
It's me who should thank you.
努力してこそ成功できます。
It is only through effort that success comes.