Why is it you're here with いんの
Grammar Explanation: Contracting いる+の to いんの

Aru returns to her classroom after club. Expecting the classroom to be empty, she’s singing a song about herself as she enters the room. There, she finds her friends idling away the time.
- アル:
- 「なな 何で皆
( いんのよ!(誰( もいないと思( ってた!)」- “Wh- why is it that you all are here?! (I was thinking no one was here!)”
- なこ:
- 「(なんだ今
( の歌( …)」- “(What was with that song just now...)”
- ソトカ:
- 「師匠
( がアルを待( つって」- “Master said she'd wait for you.”
- アル:
- 「でも私
( 部活( あるわよ」- “But I'm in a club!”
Note: Sotoka refers to Bocchi as 師匠
Key Points
いんの = contracted いるの
皆
( いんの is a casual spoken contraction of 皆( いるの.
のよ gives emotional explanatory force
Sentence-final の adds an explanatory “how come…?” feeling.
よ makes Aru’s reaction more forceful and expressive.
See Also
- Grammar: Reasoning with 〜のだ
- Kanji: Sections and departments with 部