Learn Hardcore Japanese: imouto ha neru mae ni iyahon de ongaku wo kiki nagara, syousetu wo yonde iru. - My younger sister reads a novel while listening to music with earphones before bed.

Using を with イヤホン would turn earphones into the direct object (the thing you’re listening to), which is wrong here—she’s not listening to earphones, she’s listening to music using earphones.

What does ～ながら mean in 聞きながら? How is it used?

～ながら means “while doing…” and shows two actions happening at the same time, with the same subject.

Form:
ます-stem of verb + ながら

聞く → 聞き + ながら
食べる → 食べ + ながら
歩く → 歩き + ながら

In this sentence:

音楽を聞きながら – while listening to music
小説を読んでいる – she is (habitually) reading a novel

So the meaning is:
“(She) reads a novel while listening to music (with earphones).”

Important points:

The subject of both actions must be the same person (here, 妹).
The action before ながら is usually the background action.
- Background: 音楽を聞く (listening)
- Main action: 小説を読む (reading)

Why is it 聞きながら and not 聞いてながら?

ながら attaches to the ます-stem of the verb, not the て-form.

Verb dictionary: 聞く
ます-form: 聞きます
ます-stem (the part before ます): 聞き
- ながら → 聞きながら

Using 聞いてながら would be ungrammatical in standard Japanese. The correct pattern is always:

歩きながら (from 歩く)
食べながら (from 食べる)
話しながら (from 話す)
聞きながら (from 聞く)

How does ながら decide which action is more important: listening or reading?

With AしながらBする, the action in B is usually understood as the main action, and A is what you’re doing at the same time in the background.

Here:

音楽を聞きながら – background: listening to music
小説を読んでいる – main: reading the novel

So the core activity is “reading a novel,” and the “listening to music” is something she does concurrently.

If you want to flip the focus and make listening the main action, you could say:

小説を読みながら音楽を聞いている。
She is listening to music while reading a novel.
(Here, listening is now the main action.)

What is the difference between 寝る前 and 寝る前に? Why is に used here?

前 means “before,” and に is often added when 前 is used as a time point that something happens at.

寝る前 – “before sleeping” (as a noun phrase; can modify another noun)
寝る前に～する – “do ~ before sleeping”

In this sentence:

寝る前に → before going to bed / before she sleeps
It’s functioning as a time expression for 読んでいる.

Compare:

寝る前の本 – a book (you read) before going to bed
寝る前に本を読む – read a book before going to bed

So, に is needed because 前 is marking when she reads.

What nuance does 読んでいる have here? Is it “is reading” right now or a habit like “usually reads”?

～ている can express both:

Progressive: an action in progress right now
- 今、小説を読んでいる。
  → I’m reading a novel (right now).
Habitual / repeated action: something someone does regularly
- 毎晩、小説を読んでいる。
  → I (usually) read novels every night.

In 寝る前に…読んでいる, combined with the time phrase 寝る前に (before bed), it most naturally suggests a habitual action:

My younger sister (usually / habitually) reads a novel before going to bed while listening to music.

If you just wrote 小説を読む, it would sound a bit more like a simple statement of fact or schedule rather than a current ongoing habit.

Why is 音楽 marked with を in 音楽を聞きながら?

を marks the direct object: the thing the verb directly acts on.

音楽を聞く – listen to music
- Verb: 聞く (to listen, to hear)
- Object: 音楽 (music)

So 音楽 is what she is listening to; を is the normal object marker here.

Compare:

ラジオを聞く – listen to the radio
先生の話を聞く – listen to the teacher’s talk
ニュースを聞く – listen to the news

Without を, 音楽聞く would sound wrong or at least very incomplete and unnatural in standard Japanese.

Could you say 妹は小説を読みながら、イヤホンで音楽を聞いている instead? Is that still correct?

Yes, that sentence is also grammatically correct, but the focus changes.

Original:

妹は寝る前にイヤホンで音楽を聞きながら、小説を読んでいる。
→ Main action: reading a novel.
Background: listening to music.

Alternative:

妹は寝る前に小説を読みながら、イヤホンで音楽を聞いている。
→ Main action: listening to music.
Background: reading a novel.

So both are fine; you choose based on which activity you want to treat as the main one. The ながら part is usually the background; the main clause after that is what you want to emphasize.

Why is it 妹は and not 妹が? What’s the difference here?

は marks the topic (“as for X…”) and が often marks the subject (“X is doing…” or “it is X that…”).

In everyday sentences like this, it’s very natural to use は for things like “my sister” when she is the topic of the conversation:

妹は寝る前に…読んでいる。
→ As for my younger sister, (she) reads…

If you used 妹が, it would sound like you’re emphasizing who is doing it, often in contrast to someone else:

(お兄ちゃんじゃなくて) 妹が読んでいる。
→ (Not my older brother,) it’s my younger sister who is reading.

In isolation, 妹は is the default, neutral choice for “my younger sister” as the topic.

Is 妹 automatically “my younger sister”? Why is there no 私の?

In Japanese, close family members are often understood from context and treated as belonging to the speaker unless otherwise specified.

So:

妹 is normally understood as “my younger sister” when the speaker is talking about their own family.
If you needed to be explicit or contrast it, you could say 私の妹, 友だちの妹, etc.

Japanese drops possessives (私の, 彼の, etc.) when it’s obvious whose something/someone is.

What is the role of the comma before 小説: …聞きながら、小説を読んでいる? Is it necessary?

The comma 、 in Japanese is often used to:

Mark a natural pause in pronunciation
Separate clauses or long/modifying phrases
Help readability

In 音楽を聞きながら、小説を読んでいる, the comma separates:

The ながら-clause: 音楽を聞きながら
The main clause: 小説を読んでいる

It’s not strictly required for grammaticality; you could write:

音楽を聞きながら小説を読んでいる。

But the comma makes the structure easier to see and the sentence easier to read, especially in longer sentences.