takibi ha atatakai.

It is read:

たきび　は　あたたかい。

Romanization: takibi wa atatakai

A small pronunciation note:

• は is written ha, but when it is a particle, it is pronounced wa.

This is one of the first things Japanese learners notice.

The character は normally reads ha, but when it is used as the topic particle, it is pronounced wa.

So in this sentence:

• 焚き火 = topic
• は = topic marker, pronounced wa
• 暖かい = warm

This is a standard spelling rule in Japanese grammar.

Yes, 焚き火 is one word.

It is made from:

• 焚き from the verb 焚く（たく）, meaning to burn or to make a fire
• 火（ひ / び）, meaning fire

Together, 焚き火（たきび） means bonfire or campfire.

The ひ in 火 becomes び here because of a common sound change in compounds.

は marks the topic of the sentence.

So 焚き火は暖かい means something like:

• As for bonfires, they are warm
• Bonfires are warm

In Japanese, the topic is what the sentence is talking about. It is not exactly the same as the grammatical subject in English, though it often overlaps.

Japanese often puts the topic first and the descriptive word at the end.

So:

• 焚き火 = bonfire / campfire
• は = topic marker
• 暖かい = warm

Japanese sentences often build toward the end, and the main statement frequently comes last.

English: A campfire is warm.
Japanese: Campfire + topic + warm

That word order is completely normal in Japanese.

Because 暖かい is an i-adjective, and i-adjectives can end a sentence by themselves.

So:

• 焚き火は暖かい。 = The campfire is warm.

You do not need です or another verb to make it grammatical.

You can also say:

• 焚き火は暖かいです。

This is a more polite version.

So:

• 暖かい = plain style
• 暖かいです = polite style

暖かい is an i-adjective.

You can tell because it ends in い.

That matters because i-adjectives change in their own way:

• plain present: 暖かい
• negative: 暖かくない
• past: 暖かかった
• past negative: 暖かくなかった

So this sentence is a very typical example of an i-adjective used as the predicate.

Both 暖かい and 温かい are read あたたかい, and both can mean warm, but there is a common tendency:

• 暖かい: warm in a broader sense, often climate, air, warmth around you
• 温かい: warm to the touch, body temperature, food, drinks, physical warmth

With 焚き火, 暖かい is very natural because a bonfire gives off surrounding warmth.

That said, real usage can overlap, and learners will sometimes see both in different contexts.

Yes, but the nuance changes.

• 焚き火は暖かい。 = As for bonfires, they are warm.
  This sounds like a general statement or description.

• 焚き火が暖かい。 = The bonfire is warm. / It’s the bonfire that is warm.
  This can sound more specific, contrastive, or focused, depending on context.

For a simple textbook-style sentence, は is the more expected choice.

Japanese usually does not mark singular vs. plural the way English does.

So 焚き火は暖かい。 could mean:

• The campfire is warm
• Campfires are warm

The exact interpretation depends on context.

If you are talking about one specific fire in front of you, it probably means the campfire is warm.
If you are making a general statement, it can mean campfires are warm.

Both are possible.

You may see:

• 焚き火
• たき火
• たきび

The mixed form 焚き火 is very common and easy to understand.

Japanese often allows different writing styles, especially for words that include kanji with less familiar readings.