Do you want an origami ninja star with んです
Grammar Explanation: Reasoning with 〜のだ

A couple of girls admire the foreign student Sotoka, as she has a sparkle about her. Sotoka notices the girls, mistaking their admiration as being for the origami ninja stars adorning her school bag.
- ソトカ:
- 「ほしいんですか?手裏剣」
- “Is it that you want one? This.”
Key Points
ほしいんですか asks for the reason behind what Sotoka sees
んですか asks for an explanation or confirmation, not just a bare yes-or-no fact.
Sotoka sees the girls looking at her and guesses the reason is that they want the origami ninja star.
ほしい describes wanting a thing
ほしい is used when the desired object is something you want to have.
Here the object is 手裏剣
( , the origami ninja star on her bag.
手裏剣
( works as a clarification after the questionThe main question is already complete as ほしいんですか.
Sotoka adds 手裏剣
( afterward to clarify what she thinks they might want.The furigana これ shows the spoken word is “this”, while the kanji 手裏剣
( identifies the thing she means: the origami ninja star.