1.
emphasis: it is precisely, it is ~ that
Adds strong emphasis to the preceding word or phrase, singling it out as the most important or relevant element. Often translatable as 'it is precisely ~ that' or left untranslated with emphasis.
こちらこそ、よろしくお願いします。
It's I who should be asking — pleased to meet you too.
こちらこそ is a fixed expression used to return a greeting or thanks.
こそ is an emphasis particle that singles out the preceding word as the key element. It takes the place of は, が or を, and can follow other particles and clauses (ここでこそ, 努力したからこそ).
Common patterns
- こちらこそ: It is I who should (say that) — used to return thanks, apologies, or greetings
- 今度こそ: this time for sure
- からこそ: precisely because
- てこそ: only by doing ~ (can one...)
- ～こそ～が: although ~ is true, (something contrasting)
Similar words
- は marks the topic neutrally
- が marks the subject (often new information)
- こそ highlights the word with strong emphasis, singling it out
Note: こそ replaces は, が and を; it does not stack with them. You say 彼こそ, not 彼がこそ or 彼はこそ.