nori to umebosi dake de mo, onigiri ha zyuubun oisii desu.

だけでも means something like even with just ... or even if it's only ....

In this sentence, 海苔と梅干しだけでも means:

• even with just seaweed and pickled plum
• even if all you have is seaweed and pickled plum

It gives the idea that those are very simple ingredients, but that is still enough.

Here, で shows the means/materials/ingredients used.

So:

• 海苔と梅干しだけで = with just seaweed and pickled plum
• literally, something like using only seaweed and pickled plum

This is the same で you often see for:

• tools: 箸で食べる = eat with chopsticks
• means: 電車で行く = go by train
• materials/ingredients: 卵で作る = make it with eggs

In this sentence, it is about what the onigiri has or is made with.

The も adds the nuance of even.

Compare:

• 海苔と梅干しだけで、おにぎりは十分おいしいです。
  = With just seaweed and pickled plum, onigiri is sufficiently tasty.

• 海苔と梅干しだけでも、おにぎりは十分おいしいです。
  = Even with just seaweed and pickled plum, onigiri is sufficiently tasty.

So も makes it sound a little more emphatic. It suggests:

• those ingredients may seem plain or minimal,
• but they are still enough for the onigiri to be tasty.

と is the basic particle for listing nouns, like and.

So:

• 海苔と梅干し = seaweed and pickled plum

It is a straightforward noun list. In this sentence, it names the two ingredients or fillings being talked about.

は marks おにぎり as the topic: as for onigiri...

So the sentence has the feel of:

• As for onigiri, even with just seaweed and pickled plum, it is tasty enough.

Using は gives a more general statement or opinion. It can sound like the speaker is talking about onigiri as a category, or making a broader comment about it.

If you used が, the sentence would feel more like focusing on onigiri itself as the thing that is tasty, often in a more specific context.

So here は fits well because this sounds like a general remark about onigiri.

十分 means enough, plenty, or sufficiently.

In this sentence, it works adverbially, modifying おいしい:

• 十分おいしい = sufficiently tasty
• tasty enough
• perfectly tasty

So although 十分 is often introduced as a noun or na-adjective in dictionaries, it can also function like an adverb in sentences like this.

Very natural examples:

• 十分大きい = big enough
• 十分わかる = understand well enough / fully understand
• 十分おいしい = tasty enough

おいしい is an i-adjective, so the plain form is already complete:

• おいしい = is tasty

To make it polite, you add です:

• おいしいです = is tasty / it's tasty

You do not say:

• おいしいだ ✘

That is because i-adjectives do not take だ in the present affirmative form.

So this part is just the standard polite pattern:

• い-adjective + です

Yes, very possibly.

Japanese often leaves things unsaid when they are obvious from context. A learner may feel that the sentence is a little compressed compared to English.

The full idea could be something like:

• 海苔と梅干しだけでも、具がそれだけでも、おにぎりは十分おいしいです。
• Even if the fillings are just seaweed and pickled plum, onigiri is still tasty enough.

But Japanese does not need to spell all of that out. Since 海苔 and 梅干し are naturally understood as ingredients/fillings for the onigiri, the shorter version sounds normal.

Japanese often puts conditions, setting, or context earlier in the sentence.

So the structure is roughly:

• [Even with just seaweed and pickled plum], [as for onigiri], [it is tasty enough].

This is very natural Japanese word order. The first part sets up the condition or situation before the main comment.

Yes, だけで is possible, but the nuance changes slightly.

• だけで = with just ...
• だけでも = even with just ...

So:

• 海苔と梅干しだけで、おにぎりは十分おいしいです。
  sounds more neutral.

• 海苔と梅干しだけでも、おにぎりは十分おいしいです。
  sounds more emphatic, with the feeling that those simple ingredients are surprisingly enough.

The version with も is often more natural when the speaker wants to stress that the simple option is still good.

Not exactly.

• とてもおいしい = very tasty
• 十分おいしい = tasty enough / sufficiently tasty

So とても focuses on high degree. 十分 focuses on being enough for the purpose.

That means 十分おいしい can sometimes sound more modest or practical than とてもおいしい.

In this sentence, the point is not necessarily that the onigiri is amazingly delicious. The point is that even simple ingredients are enough to make it properly tasty.

Good question. 海苔 is usually the seaweed wrapped around the outside of the onigiri, while 梅干し is commonly a filling.

So strictly speaking, they do not play the same role. But in everyday speech, Japanese can still list them together when talking loosely about what the onigiri has with it or in it.

The sentence is not trying to make a technical distinction between:

• wrapper
• filling
• ingredient

It is just saying that a simple onigiri with nori and umeboshi is already tasty enough.

So the phrasing is natural even if the roles of the two items are slightly different.