haha ha ima rusu desu.

Because 母（はは） is the usual word for my mother when you are talking about her to someone else.

A very common pattern in Japanese is:

• 母 = my mother, when referring to her from an outside perspective
• お母さん = someone else’s mother, or your own mother when addressing her directly

So if you are speaking to a teacher, neighbor, or visitor, 母は今留守です sounds natural.

By contrast:

• calling to your mother: お母さん！
• talking about your own mother to others: 母は…

This is related to Japanese social perspective: you often use a more plain or humble family term for your own family when speaking to outsiders.

In this sentence, 母 is pronounced はは.

So the full sentence is:

はは は いま るす です

This can look confusing because the written form is one kanji, but the reading is はは, not ぼ in this case.

A few useful comparisons:

• 母 → はは when it means my mother
• お母さん → おかあさん
• 母親 → ははおや

Because when は is used as the topic particle, it is pronounced わ, not は.

So in:

母 は 今 留守 です

the は after 母 is the particle, so it is read wa.

This is one of the first big pronunciation exceptions learners meet in Japanese:

• は as a normal syllable: ha
• は as a particle: wa

So the sentence sounds like:

はは は いま るす です → pronounced roughly haha wa ima rusu desu

留守（るす） means that someone is not at home or away.

In this sentence, it does not simply describe a permanent trait. It describes a current situation: your mother is out right now.

A useful nuance:

• 留守です = not home / away / out
• often used when answering the door or phone

For example, if someone asks for your mother, you might say:

母は今留守です。

That means she is currently absent, usually from home.

Also, 留守 is strongly associated with being away from the place where the person is expected to be, especially home.

Because many time expressions in Japanese can be used without a particle.

So 今 naturally fits directly into the sentence:

• 母は今留守です

This is very normal. Time words such as these often appear with no particle:

• 今日
• 明日
• 昨日
• 今

You can sometimes add a particle for contrast or emphasis, but the basic sentence usually does not need one.

For example:

• 今は = as for now / right now, at least
• 今 = simply now

So 母は今留守です is the straightforward, neutral version.

です makes the sentence polite and works like a polite copula.

In this sentence, 留守 is functioning like a na-adjective-style noun or nominal predicate, and です completes the polite statement:

• 留守です = is out / is away

Without です, the sentence would sound less polite or incomplete in standard polite speech.

Compare:

• 母は今留守です。 = polite
• 母は今留守だ。 = plain style
• 母は今留守。 = very casual, conversational

So です is not adding a new meaning so much as setting the politeness level and finishing the predicate.

Yes, Japanese word order is more flexible than English, but this order is the most natural and neutral here.

The sentence structure is basically:

• 母は = as for my mother
• 今 = now
• 留守です = is away / is not home

So:

母は今留守です

sounds very natural.

You may also hear:

• 今、母は留守です。

This is also correct. It gives 今 a little more prominence as the time setting.

Japanese often allows movement of elements like time expressions, but the most important rule is that the predicate comes at the end.

Yes. It is completely natural.

Japanese often leaves out information that is already obvious from context. With 留守, the place is usually understood as the relevant place, often home.

So you do not need to say:

• 母は今家にいません every time
• or explicitly mention at home

留守です already implies absence from the expected place.

This kind of omission is very common in Japanese. If the listener knows you are talking about the house, then 母は今留守です is enough.

You could, but the nuance changes.

• 母は今留守です = as for my mother, she is out now
• 母が今留守です = it is my mother who is out now / my mother is the one who is out now

In many everyday situations, は is the more natural choice because you are introducing my mother as the topic and then describing her current state.

が tends to sound more specific, selective, or focus-heavy. For example, it may fit if someone asked:

• 誰が留守ですか。
  母が今留守です。

So for a normal statement to a visitor or caller, 母は今留守です is usually the better default.

Yes. It is polite but not overly formal.

The politeness mainly comes from です. This makes it suitable for many everyday situations, such as speaking to:

• a visitor
• a caller
• a teacher
• a neighbor
• a coworker

It is a very common practical sentence.

If you wanted to sound even more formal or business-like, you might hear expressions such as:

• 母はただいま席を外しております in a workplace-type setting
• or other more formal absence expressions

But for ordinary daily conversation, 母は今留守です is polite and natural.

Yes, in many situations you could say:

母は今いません。

That means my mother is not here / is not present now.

The difference is nuance:

• 留守です emphasizes being out / away from home
• いません simply says is not here

So if someone calls your house or comes to your door, 留守です often sounds especially natural because it matches that situation well.

Compare:

• 母は今留守です。 = my mother is out right now
• 母は今いません。 = my mother isn’t here right now

Both are correct, but 留守です has a stronger not at home / away feeling.