〜こそ
Precisely 〜こそ
Meaning
Singles something out for emphasis — "this is the one that ~", "precisely ~".
Formation
[noun] + こそ · [て-form] + こそ · 〜からこそ (that is exactly why)
Notes
Replaces は or が and puts the spotlight on that word: 今年こそ合格したい ("this year is the year I pass"). こちらこそ is the set reply to thanks or greetings. からこそ gives an emphatic reason: あなただからこそ話すのです.
Examples
今年（ことし）こそ日本語能力試験（にほんごのうりょくしけん）に合格（ごうかく）したいです。
This year is the year I want to pass the JLPT.
Breakdown
いいえ、こちらこそありがとうございます。
No, thank YOU. (the set reply)
Breakdown
努力（どりょく）したからこそ成功（せいこう）したのです。
It is precisely because he worked hard that he succeeded.
Breakdown
これこそ私（わたし）が探（さが）していた本（ほん）です。
This is exactly the book I was looking for.
Breakdown
困（こま）った時（とき）こそ助け合（たすけあ）うべきです。
It is when times are hard that we should help one another.
Breakdown
⚠️ Often confused with
〜くらい / 〜ぐらい
About / to the extent 〜くらい
An approximate amount — "about ~" — or a degree — "to the extent that ~".
〜ば〜ほど
The more … the more 〜ば〜ほど
"The more ~, the more ~" — one thing increases as another does.
〜ほど / 〜ほどだ
To the extent 〜ほど
Gives a yardstick for how much — "so ~ that …", "to the extent of ~".
〜さえ / 〜でさえ
Even 〜さえ
Picks an extreme example — "even ~". If this much is true, the rest follows.
〜てまで / 〜までして
Even going so far as 〜てまで
"Even going so far as to ~".
〜極まりない
Utterly extreme 〜極まりない
"Extremely ~", "~ in the extreme" — an emphatic, usually critical judgement.
〜といったらない
Beyond description 〜といったらない
"Indescribably ~", "~ beyond words" — an exclamation of extremity.
〜始末だ
Ending up badly 〜始末だ
"It ended up ~ (of all things)" — a bad process reaches a worse conclusion.