kuukou ni ku tukitai node, asita ha sihatu ni noru tumori desu.

Because 早く is the adverb form of the い-adjective 早い.

• 早い = early / fast
• 早く = early / quickly

Here, 早く modifies the verb 着きたい, so it means want to arrive early.

• 早い電車 = an early train
• 早く着きたい = want to arrive early

着きたい is the たい-form of 着く, which means to arrive.

So:

• 空港に行きたい = I want to go to the airport
• 空港に着きたい = I want to arrive at the airport

This sentence focuses on arriving early, not just going there.

It comes from the verb 着く.

Steps:

1. 着く is a u-verb
2. Change く to the i-stem: 着き
3. Add たい

So:

• 着く → 着きたい = want to arrive

The たい form behaves like an い-adjective, which is why it can connect to ので in a natural way.

The particle に marks the destination with verbs like 着く.

So:

• 空港に着く = arrive at the airport

With 着く, に is the normal particle because it marks the place where you end up.

Usually, with 着く, に is preferred.

• 空港に着く = natural and standard
• 空港へ着く = generally not the usual phrasing

へ emphasizes direction toward a place, while 着く is about arrival at a place, so に fits better.

ので means because or so.

In this sentence:

• 空港に早く着きたいので = because I want to arrive at the airport early

Compared with から:

• ので sounds a little softer, more explanatory, and often more polite
• から can sound more direct or more like a personal reason

So both can work, but ので fits well in calm explanations.

• 早く着きたいので、始発に乗るつもりです。
• 早く着きたいから、始発に乗るつもりです。

Both are grammatical, but the first sounds a bit gentler.

は marks 明日 as the topic: as for tomorrow.

So the sentence has a structure like:

• As for tomorrow, I plan to take the first train, because I want to arrive at the airport early.

Using は helps set the time frame as the topic of the sentence.

If you used 明日 without は, the sentence would still be understandable in some contexts, but 明日は sounds more natural when introducing tomorrow as the relevant time.

始発 means the first departure of the day.

Depending on context, it can mean:

• the first train
• the first subway
• the first bus

In a sentence like this, 始発に乗る usually means take the first train / first available service of the day.

Because the verb is 乗る, and with 乗る, the thing you get on is marked by に.

• 電車に乗る = ride/get on a train
• バスに乗る = ride/get on a bus
• 始発に乗る = take the first departure

So this に is different from the に after 空港:

• 空港に = destination of arrival
• 始発に = thing you board

つもりです means intend to or plan to.

So:

• 始発に乗るつもりです = I intend to take the first train

It expresses a personal intention or plan.

This is a very common pattern:

• dictionary form + つもりです

Examples:

• 行くつもりです = I intend to go
• 勉強するつもりです = I intend to study
• 早く寝るつもりです = I plan to sleep early

Because つもりです attaches to the plain/dictionary form of the verb, not the ます-form.

So:

• 乗るつもりです = correct
• 乗りますつもりです = incorrect

This is true for many grammar patterns in Japanese: even in polite speech, the verb before the pattern is often in plain form.

This is very normal in Japanese.

Inside the sentence, grammar patterns often use plain forms:

• 着きたいので
• 乗るつもりです

The overall sentence is still polite because it ends with です.

Japanese politeness is often shown mainly at the end of the sentence, not by making every verb polite.

Yes, the natural subject is I, even though it is omitted.

Japanese often leaves out subjects when they are obvious from context. Since the sentence says:

• 着きたい = want to arrive
• 乗るつもりです = intend to take

it is most naturally understood as the speaker’s own wish and plan:

• I want to arrive at the airport early, so tomorrow I plan to take the first train.

The comma after ので is mainly there to make the sentence easier to read.

• 空港に早く着きたいので、明日は始発に乗るつもりです。

It marks a natural pause between:

1. the reason
2. the main action/plan

It is helpful, but in many cases Japanese punctuation is a little flexible, especially in casual writing.

Yes, but the nuance changes a little.

• 早く着きたい = want to arrive early
• 早めに着きたい = want to arrive a bit early / relatively early

早めに often suggests earlier than usual or with some extra margin.
早く is more straightforward and direct.

So both can work, but 早く is perfectly natural here.