particle
it is ... that ...; precisely; definitely
Emphasizes the preceding word or phrase, often contrastively. Common in patterns like ～こそ～が, ～からこそ, and set phrases such as こちらこそ.
今年こそ、日本語をマスターしたい。
This year, I definitely want to master Japanese.
こちらこそ、よろしくお願いします。
It is I who should say that; pleased to meet you.
particle
although; while; it is the case that ... but
Used in the patterns こそあれ, こそすれ, こそするが, etc., to acknowledge a fact while contrasting it with another. Slightly formal or literary.
苦労こそあれ、得るものも大きい。
Although there are hardships, what you gain is also great.
particle
precisely because; only because
Follows the conditional -ba form of a verb, emphasizing that the reason given is the very cause. Often used in explanations or justifications.
努力すればこそ、成功がある。
It is precisely because you make an effort that success comes.
particle
not at all; absolutely not; never
Formal or literary. Follows the -nai stem of a verb + ば, creating a strong negative expression. Often used in emphatic denial.
彼の決意は揺るがばこそ。
His determination will not waver in the slightest.