haru ha kahun no sei de, hanamizu ga tomaranai hi ga arimasu.

は marks 春 as the topic: As for spring... or In spring...

So the sentence is setting the scene first:

• 春は = In spring / As for spring
• then it says what happens during that time

This is very common in Japanese. A literal structure is:

• As for spring, there are days when...

Even though English often uses in spring, Japanese often uses 春は to introduce the seasonal topic.

花粉のせいで means because of pollen or due to pollen.

Breakdown:

• 花粉 = pollen
• の = links the noun to せい
• せい = cause/blame, often with a negative result
• で = because of / due to

So 花粉のせいで is not just a neutral cause. It often carries a feeling like:

• because of this troublesome thing
• thanks to this annoying cause (but in a negative way)

That fits well here, because runny noses are unpleasant.

Usually, yes. せい tends to be used when the result is bad, inconvenient, or frustrating.

Examples:

• 雨のせいで、試合が中止になった。
  The game was canceled because of the rain.
• 花粉のせいで、鼻水が止まらない。
  Because of pollen, my nose won’t stop running.

If the result is positive, Japanese usually uses something else, such as:

• おかげで = thanks to

So:

• 花粉のせいで = because of pollen, unfortunately
• 先生のおかげで合格した = I passed thanks to my teacher

In X のせいで, the で helps connect the cause to the result.

Pattern:

• Noun + のせいで + result

Examples:

• 風邪のせいで学校を休んだ。
  I missed school because of a cold.
• 渋滞のせいで遅れた。
  I was late because of traffic.

You can think of のせいで as one set phrase meaning because of with negative nuance.

There is also X のせいだ, which is more like:

• It is X’s fault
• The cause is X

For example:

• 遅刻したのは電車のせいだ。
  The reason I was late was the train.

Here, が marks 鼻水 as the thing that is doing the action/state of not stopping.

• 鼻水が止まらない = my runny nose won’t stop / the nasal discharge doesn’t stop

This is a very natural pattern in Japanese:

• 涙が止まらない = the tears won’t stop
• 咳が止まらない = the coughing won’t stop
• くしゃみが止まらない = the sneezing won’t stop

Using は would change the nuance. It might sound contrastive, like:

• As for the runny nose, it won’t stop
  (possibly contrasting it with something else)

So が is the normal choice here.

Literally, 止まらない means does not stop.

Breakdown:

• 止まる = to stop
• 止まらない = does not stop

In this sentence, it describes 鼻水:

• 鼻水が止まらない = the runny nose doesn’t stop

English usually says:

• my nose won’t stop running
• I have a runny nose that won’t stop

Japanese expresses it more literally as nasal discharge does not stop.

Not exactly word-for-word, but it matches the meaning well in context.

• 鼻 = nose
• 水 = water
• 鼻水 literally means nose water, meaning mucus / nasal discharge / snot

In natural English, 鼻水が止まらない is often translated as:

• my nose won’t stop running
• I have a runny nose

So 鼻水 is the stuff itself, while English often describes the condition instead.

日 means day, and here it means days when that happens.

The structure is:

• [clause] 日がある / 日があります

So:

• 鼻水が止まらない日 = days when my nose won’t stop running
• 鼻水が止まらない日があります = there are days when my nose won’t stop running

This is a very common way to make a noun phrase in Japanese:

• 雨が降る日 = a day when it rains
• 忙しい日 = a busy day
• 学校がない日 = a day when there is no school

日がありません / 日があります is the normal way to say there are days...

Here, 日 is the thing that exists, so it takes が:

• 日がある = there are days
• そういう日がある = there are such days

The sentence is simply making a statement, so it ends with あります.

Using は would sound more contrastive or topical:

• 鼻水が止まらない日はあります。
  As for days when my nose won’t stop running, there are some.

That is possible, but it has a different emphasis. 日があります is the straightforward neutral form.

Because the sentence is saying that something exists:

• 鼻水が止まらない日がある = there are days when my nose won’t stop running

The verb ある is used for inanimate things or abstract things that exist, including:

• days
• time
• events
• chances
• reasons

So あります is the polite form of ある.

If you ended with です, the structure would need to be different.

A helpful way to see it is:

• 春は = as for spring / in spring
• 花粉のせいで = because of pollen
• 鼻水が止まらない = my nose won’t stop running
• 日が = days
• あります = there are

So the whole structure is:

• As for spring, because of pollen, there are days when my nose won’t stop running.

Japanese often builds long noun phrases before the main noun:

• 鼻水が止まらない日 = days when my nose won’t stop running

That whole chunk then becomes the thing that exists.

Yes, the affected person is implied from context.

Japanese often leaves out subjects and possessives when they are obvious. So:

• 鼻水が止まらない literally = the nasal discharge doesn’t stop
• natural English = my nose won’t stop running

In most situations, listeners understand that the speaker is talking about their own symptoms unless something else is stated.

If needed, Japanese could make it explicit:

• 私は春は花粉のせいで、鼻水が止まらない日があります。
  As for me, in spring, there are days when my nose won’t stop running because of pollen.

But usually that 私は is unnecessary.

Yes, 花粉で is possible in some contexts, but 花粉のせいで gives a stronger feeling that pollen is the troublesome cause.

Compare:

• 花粉で鼻水が出る。
  I get a runny nose from pollen.
• 花粉のせいで鼻水が止まらない。
  Because of pollen, my nose won’t stop running.

So のせいで adds more of a this annoying thing is causing it nuance.

Yes, that is completely okay.

This sentence has:

• 鼻水が止まらない
• 日があります

The first が belongs to the inner clause:

• 鼻水が止まらない = the runny nose won’t stop

The second が marks the main subject of the larger sentence:

• 鼻水が止まらない日がある = there are days when the runny nose won’t stop

So the first clause modifies 日, and then 日 becomes the thing that exists.

This kind of nested structure is very common in Japanese.

No. 日があります means there are days like that, not every day.

So the nuance is:

• sometimes in spring
• on some spring days
• there are days when this happens

If the speaker wanted to say it happens all the time, they would use a different expression, such as:

• 春はいつも花粉のせいで鼻水が止まらない。
  In spring, my nose never stops running because of pollen.
• 春になると毎日つらい。
  When spring comes, every day is miserable.

So 日があります suggests occasional or recurring days, not constant suffering.