imouto ga gakkarishite ita node, watashi wa daijoubu da yo to itte nagusameta.

topic particle

Breakdown of imouto ga gakkarishite ita node, watashi wa daijoubu da yo to itte nagusameta.

• 私わたし: I
• が: subject particle
• 大丈夫だいじょうぶ: okay

Questions & Answers about imouto ga gakkarishite ita node, watashi wa daijoubu da yo to itte nagusameta.

Why is が used after 妹 instead of は?

In 妹ががっかりしていたので, 妹が marks younger sister as the subject of the clause was disappointed.

Using が here is very natural because:

• it introduces who was in that emotional state
• it keeps the focus on the sister inside the reason clause

If you changed it to 妹は, it would sound more like you were setting up as for my sister..., which gives a slightly different contrastive/topic feeling.

So in this sentence, が is the straightforward subject marker for the subordinate clause.

What does がっかりしていた mean grammatically? Why not just がっかりした?

がっかりする means to be disappointed.

Here, がっかりしていた is the te-form + いる pattern in the past:

• がっかりしている = is disappointed / is in a disappointed state
• がっかりしていた = was disappointed / was in a disappointed state

This often describes an ongoing state or condition in the past, not just a one-time moment of becoming disappointed.

So:

• がっかりした can sound more like became disappointed
• がっかりしていた emphasizes that she was in that disappointed state when the speaker responded

What is the role of ので in this sentence?