sentence-final particle for emphasis
Familiar, masculine-leaning particle that strengthens a question, assertion, or invitation. Similar to かい, だい, and わい, but with a blunt, emphatic feel. Often used in casual male speech.
何してるんだい？
What are you doing?
そんなことあるかい。
Is that really the case?
Kana-only sentence-final particle; no kanji form exists.
The exact derivation is uncertain; it may be a contraction of かい or a related emphatic particle. It is used in familiar, often masculine, speech.