Learn Hardcore Japanese: nihonzin ha sinsetu desu.

So the whole sentence is like saying: “As for Japanese people, they are kind.”
That is why it naturally comes across as a general statement about Japanese people.

Does 日本人 mean “Japanese person” or “Japanese people”?

日本人 can mean both “a Japanese person” and “Japanese people”. Japanese usually does not mark plural on nouns (no s like in English).

Which one it is depends on context:

In 日本人は親切です, with は and no other context, the most natural reading is a generalization:
→ “Japanese people are kind.”
If you want to clearly say one person, you could say 一人の日本人 (one Japanese person).
If you want to emphasize plurality, you can say 日本人たち, but for general statements like this, plain 日本人 is normal.

Why is は pronounced wa here and not ha?

In Japanese spelling, the character は is normally read ha, but when it is used as the topic particle, its pronunciation changes to wa.

So:

As part of a word: 花 (はな / hana) = flower
As the topic particle: 日本人は (にほんじんは / nihonjin wa)

This is just an irregular historical spelling convention you have to memorize:
topic particle は → pronounced “wa.”

What does です mean here? Is it like “is/are/am”?

です is the polite copula, often taught as the polite form of the verb “to be”.

In this sentence:

親切です corresponds roughly to “is kind / are kind” in English.
The です adds politeness, not formality in a business sense, but basic respectful speech.

Very roughly:

親切だ → “is/are kind” (plain, casual)
親切です → “is/are kind” (polite)

So 日本人は親切です is a polite way to say “Japanese people are kind.”

Is 親切 a noun or an adjective?

親切 is a na‑adjective (な‑adjective) in Japanese.

Na‑adjectives behave a bit like both nouns and adjectives:

Before a noun:
- 親切な人 → a kind person
  (here it works like an adjective)
As a predicate with だ／です:
- その人は親切です。 → That person is kind.
  (used like “kind” in English)
As a noun meaning “kindness” in some contexts:
- 親切にありがとう。 → Thank you for your kindness.

In 日本人は親切です, 親切 functions as “kind” (an adjective idea) describing 日本人.

Why is it 親切です and not 親切なです?

For na‑adjectives like 親切, な is only used directly before a noun:

親切な人 → a kind person
静かな町 → a quiet town

But when you use a na‑adjective as a predicate with だ／です, you do not use な:

日本人は親切です。 ✔
日本人は親切なです。 ✘ (incorrect)

So the pattern is:

[na‑adjective] + な + noun → 親切な人
[na‑adjective] + だ／です → 親切です

Could this sentence mean “I am a kind Japanese person”?

Normally, no. On its own, 日本人は親切です is naturally understood as a general statement:

“Japanese people are kind.”

If you wanted to say “I am a kind Japanese person”, you would usually mark yourself as the topic or subject:

私は親切な日本人です。 → I am a kind Japanese person.
私は日本人で、親切です。 → I’m Japanese and I’m kind.

Using 日本人は親切です to mean “I am a kind Japanese person” would sound unnatural and confusing.

How would this sentence change in casual (informal) speech?

In casual speech, you usually replace です with だ, or even drop it in some contexts.

Common casual versions:

日本人は親切だ。 → plain form, neutral casual
日本人って親切だよね。 → more conversational: Japanese people are really kind, huh.

Using 日本人は親切です is still fine in everyday conversation; it’s just polite rather than plain. Which you choose depends on who you’re talking to and the level of formality.

Does this sentence mean all Japanese people are kind?

Literally, 日本人は親切です is a general statement, so it can sound like:

“Japanese people are kind (as a group / in general).”

However, in real usage, such statements are often understood as a broad tendency or stereotype, not a mathematically absolute “every single one”.

If you want to soften it and make it clear you mean “many” or “tend to be,” you can say things like:

日本人は親切な人が多いです。
→ Many Japanese people are kind.
日本人には親切な人が多いです。
→ Among Japanese people, there are many kind people.

How would I say “Japanese people are not kind” or “Japanese people are very kind”?

Starting from 日本人は親切です:

Negative:

Polite: 日本人は親切ではありません。
More colloquial: 日本人は親切じゃありません。
Plain: 日本人は親切ではない／親切じゃない。

All mean roughly: “Japanese people are not kind.”

“Very kind”:

Just add an adverb like とても or すごく before 親切:

日本人はとても親切です。 → Japanese people are very kind.
日本人はすごく親切です。 → Japanese people are really kind.

What is the difference between 日本人は親切です and 日本人が親切です?

Both contain 日本人 and 親切です, but the particle changes the nuance.

日本人は親切です。
- は marks the topic.
- Natural as a general statement: As for Japanese people, they are kind.
日本人が親切です。
- が marks a more specific subject or picks something out.
- Often used in contrast or in answer to a “who?” question, like:
  - 誰が親切ですか。 → Who is kind?
  - 日本人が親切です。 → The Japanese (people) are the ones who are kind.

In beginner-friendly terms: は is “as for / speaking of…”, and が is more like pointing out who actually is [kind] in that context.