imouto ha ookina inu wo kowagaru keredo, tiisai inu nara issyo ni asobitagaru.

In Japanese, words like 妹 often do not need an explicit my when the context is clear. In a normal sentence like this, 妹 is naturally understood as my younger sister.

A few useful points:

• 妹 = younger sister
• 姉 = older sister
• Japanese often leaves out possessives like my, your, or his if they are obvious from context.

So here, 妹は... is most naturally understood as As for my younger sister, ...

は marks 妹 as the topic of the sentence.

So 妹は means something like:

• As for my younger sister, ...
• My younger sister, ...

It does not simply mark the subject in a mechanical way; it sets up what the sentence is about. In this sentence, everything that follows is describing your younger sister’s behavior:

• she is afraid of big dogs
• but with small dogs, she wants to play

There is also a slight contrastive feeling because the sentence later contrasts big dogs with small dogs.

Yes, both 大きい犬 and 大きな犬 are possible.

In this sentence, 大きな犬 is used because 大きな can function directly before a noun and often sounds a little more descriptive or literary. In many everyday contexts, the difference is small.

So:

• 大きい犬 = a big dog
• 大きな犬 = a big dog

Likewise:

• 小さい犬 = a small dog
• 小さな犬 = a small dog

One thing learners often notice is that 大きい / 小さい can be used either as ordinary -い adjectives or in the special forms 大きな / 小さな before nouns.

This is a very common question.

• 怖い means scary or afraid as an adjective.
• 怖がる is a verb meaning to be afraid of, to show fear toward, or to act scared of.

With third-person subjects, Japanese often prefers 怖がる when describing someone else’s observable behavior.

Compare:

• 私は犬が怖い。 = I am afraid of dogs.
• 妹は犬を怖がる。 = My younger sister is afraid of dogs / acts scared of dogs.

Because the speaker can directly state their own feelings more naturally, 怖い works well for I. But for someone else’s internal feelings, Japanese often uses a verb like 怖がる, which is based on what can be observed.

Because 怖がる is a verb, the thing someone fears is commonly marked with を.

So:

• 犬を怖がる = to be afraid of dogs

This is different from 怖い, where the thing causing fear is often marked with が:

• 犬が怖い = dogs are scary / I am afraid of dogs

So the particle pattern changes with the grammar:

• 怖い → often が
• 怖がる → often を

That difference is very common and worth getting used to.

けれど means but, though, or however.

It connects the two contrasting parts of the sentence:

• 妹は大きな犬を怖がるけれど、
• 小さい犬なら一緒に遊びたがる。

So the contrast is:

• she is afraid of big dogs
• but when it comes to small dogs, she wants to play

In casual conversation, you might also hear:

• けど
• でも (used a little differently, usually at the start of a new clause/sentence)

Here, けれど smoothly links two clauses in one sentence.

なら here sets up a condition or topic-like frame: if it’s a small dog, when it comes to small dogs, or as for small dogs.

So 小さい犬なら can be understood as:

• if it’s a small dog
• when it comes to small dogs
• as long as the dog is small

It contrasts with 大きな犬 from the first half.

That means the sentence is not saying she wants to play with every dog. It is saying that small dogs are a different case.

This is another important grammar point.

• 〜たい expresses the speaker’s own desire very directly.
• 〜たがる is often used for someone else’s apparent desire.

So:

• 私は遊びたい。 = I want to play.
• 妹は遊びたがる。 = My younger sister seems to want to play / shows that she wants to play.

Because the sentence is talking about 妹 (a third person from the speaker’s perspective), 遊びたがる is the natural choice.

Japanese often avoids stating another person’s inner feelings too directly, so 〜たがる is used to describe what their behavior suggests.

一緒に means together.

So 一緒に遊ぶ means:

• to play together
• to play with someone

In this sentence, the person she wants to play together with is understood from context to be the small dog.

So even though the dog is not repeated in the second clause, the meaning is:

• With small dogs, she wants to play together with them.

Because Japanese often omits words that are easy to understand from context.

The second half says:

• 小さい犬なら一緒に遊びたがる。

The listener naturally understands that the missing partner in play together is the small dog just mentioned.

In English, we might be more likely to say:

• ...but if it’s a small dog, she wants to play with it.

In Japanese, that object or partner can be left unstated if it is obvious.

It can feel like either in English, depending on how you translate it.

The Japanese gives a contrastive frame with なら, so the core idea is:

• when it comes to small dogs, she wants to play
• if the dog is small, she wants to play

Both capture the meaning well.

A very natural English translation would be:

• My younger sister is afraid of big dogs, but if it’s a small dog, she wants to play with it.

That translation brings out the contrast most clearly.

Yes. The sentence sounds like the speaker is describing a pattern in the younger sister’s behavior:

• big dogs scare her
• small dogs make her want to approach and play

The use of 怖がる and 遊びたがる both gives the feeling of observed behavior, which is very natural when talking about another person.

So the sentence is not just about abstract facts. It sounds like the speaker has watched the younger sister react differently depending on the size of the dog.