ani ha arukuno ga osoi node, watasi ha saki ni eki ni ikimasu

When talking about your own older brother to someone else, Japanese normally uses 兄. Using お兄さん for your own brother sounds too respectful in most neutral situations.

A useful rule of thumb:

• 兄 = my older brother
• お兄さん = someone else’s older brother, or a respectful/casual way to refer to an older-brother figure

So in this sentence, 兄は… is the natural choice.

Both は particles mark topics, but they do slightly different jobs here.

• 兄は sets up the first topic: as for my older brother
• 私は then marks the speaker as the topic of the main action: as for me

So the sentence is structured a bit like this:

• As for my older brother, he walks slowly, so
• as for me, I’ll go to the station first.

The second は can also create a mild contrast:

• he is slow
• I, therefore, will go ahead

の turns the verb 歩く into a noun-like phrase.

• 歩く = to walk
• 歩くの = walking / the act of walking

So:

• 歩くのが遅い literally means the walking is slow
• in natural English, that becomes walks slowly or is slow at walking

This is a very common pattern in Japanese:

• V + の + が + adjective

Examples:

• 食べるのが早い = is fast at eating / eats quickly
• 話すのが上手 = is good at speaking

In 歩くのが遅い, the が marks 歩くの as the thing being described by 遅い.

So the structure is:

• 歩くの = walking
• が = subject marker
• 遅い = slow

This means walking is slow.

If you said 歩くのは遅い, that would put extra topic/contrast emphasis on walking. It can be grammatical, but it sounds different, something like:

• As for walking, he’s slow
• When it comes to walking, he’s slow

In this sentence, が is the more neutral and natural choice.

It is understood to be 兄.

Japanese often leaves out information that is clear from context. Since the sentence begins with 兄は, the listener naturally understands that the whole description 歩くのが遅い is about the older brother.

So although Japanese does not repeat 兄が歩くのが遅い, the meaning is still clear:

• My older brother is slow at walking

ので means because / since, but it often sounds a bit softer, more explanatory, and less direct than から.

So:

• 遅いので、私は先に駅に行きます = Because he walks slowly, I’ll go to the station first

Compared with から:

• から can sound more straightforward, assertive, or personal
• ので often sounds more neutral and matter-of-fact

In many situations both are possible, but ので is common when giving a reason politely or gently.

Before ので, Japanese normally uses the plain form of verbs and adjectives.

So:

• 遅いので = because it is slow
• not 遅いですので in ordinary sentence structure

For い-adjectives, the plain form is just the basic dictionary form, so 遅い is exactly what you expect here.

The sentence can still end politely with 行きます, even though the earlier clause is plain. This mix is very normal in Japanese.

先に means ahead, first, or before someone else.

Here, it means that the speaker will go to the station before the older brother arrives there or without waiting for him.

So the nuance is not just early in general. It is more like:

• I’ll go on ahead to the station
• I’ll go to the station first

The に turns 先 into an adverbial expression:

• 先 = ahead / earlier
• 先に = ahead / first

Yes, 駅へ行きます would also be possible.

Both に and へ can mark the destination of movement verbs like 行く.

Very roughly:

• 駅に行く = go to the station
• 駅へ行く = go toward/to the station

The difference is usually small here.

• に often feels like a straightforward destination marker
• へ can slightly emphasize direction

In everyday speech, 駅に行きます is extremely common and natural.

Yes, but the nuance would change.

• 兄は歩くのが遅いので… = As for my older brother, he walks slowly, so…
• 兄が歩くのが遅いので… = Because my older brother is the one who walks slowly…

Using は makes 兄 the topic and sounds more natural in a general statement about him.

Using が would put more focus on 兄 as the subject, possibly in contrast to someone else. For example, it could sound like:

• My older brother is the one who is slow, so…

In this sentence, は is the most natural choice.

Not exactly.

• 歩くのが遅い = slow at walking / walks slowly
• 足が遅い = has slow legs; commonly means runs slowly or is bad at moving quickly
• 歩くのが下手 = bad at walking, which suggests lack of skill rather than just speed

So in this sentence, 歩くのが遅い specifically focuses on walking speed.

It breaks down like this:

• 兄は = as for my older brother
• 歩くのが遅い = walking is slow / he walks slowly
• ので = because / since
• 私は = as for me
• 先に = first / ahead
• 駅に行きます = will go to the station

So the full logic is:

My older brother walks slowly, so I’ll go to the station first.

A more natural English translation could also be:

• My older brother walks slowly, so I’ll go on ahead to the station.