asita no maturi ni ha, aoi yukata wo kite ikimasu.

In Japanese, many common time words can appear without any particle. 明日, 今日, 昨日, 来年, and similar words often work this way.

So:

• 明日 祭りに行きます = I will go to the festival tomorrow.
• 明日に is usually unnatural here.

A rough rule:

• specific clock times / dates often take に
  
  • 3時に = at 3 o’clock
  • 金曜日に = on Friday
• relative time words often do not
  
  • 明日 = tomorrow
  • 来週 = next week

So 明日 in this sentence is completely normal without a particle.

Here, の links two nouns together.

• 明日 = tomorrow
• 祭り = festival
• 明日の祭り = tomorrow’s festival / the festival tomorrow

This の is often taught as a possessive marker, but it does more than show possession. It can also connect nouns in a descriptive way.

So 明日の祭り does not mean that tomorrow owns the festival. It just means the festival that is tomorrow.

には is a combination of:

• に = to / at / for, depending on context
• は = topic marker, often with a slight contrast or emphasis

So 祭りには means something like:

• as for the festival tomorrow...
• to the festival, at least...
• when it comes to the festival tomorrow...

In this sentence, に is there because 行きます uses a destination marker. The added は makes the festival phrase into a topic and can add a small sense of contrast or emphasis.

Compare:

• 祭りに行きます = I’m going to the festival.
• 祭りには行きます = I am going to the festival, at least / as for the festival, I am going.

In many cases, the English translation may not show this difference clearly, but the nuance is there in Japanese.

Japanese non-past forms often cover both:

• present
• future

So いきます can mean:

• go
• will go

The time word 明日 tells you this is future, so いきます is naturally understood as will go.

This is very common in Japanese:

• 明日、学校に行きます。 = I will go to school tomorrow.
• 来週、会います。 = I will meet them next week.

Japanese usually does not need a separate future tense form the way English does.

青い is an い-adjective, and it directly modifies the noun:

• 青い浴衣 = a blue yukata

This is the most straightforward and natural way to say it.

You may also see things like 青の〜, but that is a different structure, where 青 is treated more like a noun. It can sound more stylistically marked or category-like depending on context.

For a beginner, the safest pattern is:

• 赤い服 = red clothes
• 白いシャツ = a white shirt
• 青い浴衣 = a blue yukata

So this sentence uses the standard adjective form.

Because 浴衣 is the thing being worn, and with the verb 着る meaning to wear, the clothing item is marked as the direct object.

• 浴衣を着る = to wear a yukata
• 服を着る = to wear clothes
• シャツを着る = to wear a shirt

So in this sentence:

• 青い浴衣を着ていきます means
• I will go wearing a blue yukata / I will put on a blue yukata and go

Even though English says wear without making the clothing sound very object-like, Japanese uses を normally here.

This is one of the most important parts of the sentence.

It is made from:

• 着る = to wear / to put on
• 着て = the て-form
• いく = to go

So 着ていく literally has the sense of:

• put on and go
• go wearing
• take that state with you as you go

In this sentence, it means the speaker will go to the festival wearing the yukata.

The nuance is not just I will wear a yukata in general. It is specifically tied to the action of going.

So:

• 青い浴衣を着ます = I will wear a blue yukata.
• 青い浴衣を着ていきます = I will go wearing a blue yukata / I will put on a blue yukata and head over.

Because 着ていきます adds a useful nuance.

• 着ます only tells you about wearing the yukata.
• 着ていきます tells you that the speaker will wear it for the purpose of going there, or go there in that outfit.

It connects the clothing choice with the upcoming event.

So the sentence is not just about clothes. It is about the speaker’s plan for attending the festival.

A natural English equivalent is often:

• I’m going to wear a blue yukata to the festival tomorrow.

But grammatically, the Japanese is closer to:

• I’ll go to tomorrow’s festival wearing a blue yukata.

Japanese often leaves out the subject when it is obvious from context.

So this sentence does not explicitly say:

• I
• we
• she
• etc.

But because this sounds like someone talking about their own plan, the natural interpretation is I.

Japanese frequently omits information that English usually includes. If the context already makes the subject clear, saying it can be unnecessary.

So this sentence is normal as-is:

• 明日の祭りには、青い浴衣を着ていきます。

It naturally means:

• I’ll go to tomorrow’s festival wearing a blue yukata.

Yes, in many cases へ can also mark direction with 行く.

So you could have:

• 祭りへ行きます = I will go to the festival.
• 祭りに行きます = I will go to the festival.

The difference is often small:

• へ emphasizes direction toward
• に often feels a little more like destination

In this sentence, に is very natural and common. Since the sentence has には, replacing it with へは is possible, but には is the more standard choice here.

Japanese word order is often different from English, and this sentence is a good example.

Break it down like this:

• 明日の祭りには = as for tomorrow’s festival
• 青い浴衣を = a blue yukata
• 着ていきます = will go wearing / will put on and go

A very literal order would be:

• As for tomorrow’s festival, a blue yukata will wear-and-go.

Of course, that sounds unnatural in English, but it shows the Japanese structure:

1. time-related phrase
2. place/topic phrase
3. object
4. verb at the end

Japanese usually puts the main verb at the end of the sentence, which is one of the biggest structural differences from English.

The comma is mainly there to show a pause and make the sentence easier to read.

• 明日の祭りには青い浴衣を着ていきます。
• 明日の祭りには、青い浴衣を着ていきます。

Both are fine.

The version with the comma slightly highlights the topic phrase 明日の祭りには before moving on to the rest of the sentence. It can sound a bit more natural in writing when the topic is set off first.

So the comma is not changing the grammar; it is mostly helping with rhythm and readability.