kinoko ga haitta pura ha karukute, sohu mo okawarisite imasita.

Here, きのこが入った is a clause modifying 天ぷら.

• 入る means to enter / to be included / to be in
• In that clause, きのこ is the thing that entered / is included
• So きのこ is the subject of 入った, which is why it takes が

So:

• きのこが入った天ぷら = tempura that had mushrooms in it / tempura containing mushrooms

A learner might expect を, but 入る is an intransitive verb, so it does not take a direct object with を in this use.

This is a relative clause: a clause placed before a noun to describe it.

So:

• きのこが入った = that mushrooms were included in
• 天ぷら = tempura

Together:

• きのこが入った天ぷら = the tempura that had mushrooms in it

Japanese does this very often. Instead of using a word like that or which, Japanese simply puts the describing clause directly before the noun.

Examples of the same pattern:

• 昨日買った本 = the book I bought yesterday
• 父が作った料理 = the dish my father made

Not necessarily. In a relative clause, the past form often describes a completed action that results in the noun’s current state.

So きのこが入った天ぷら does not have to mean tempura that used to have mushrooms. It naturally means tempura with mushrooms in it.

Why 入った works well:

• it presents the mushrooms as something that were put in / came to be included

Why 入っている might also be possible:

• きのこが入っている天ぷら would emphasize the state of containing mushrooms

The difference is subtle here:

• 入った = slightly more compact, often very natural in descriptions
• 入っている = slightly more explicit about the current state

The whole phrase きのこが入った天ぷら is the topic of the sentence, so は comes after the entire noun phrase.

• きのこが入った天ぷらは = as for the tempura with mushrooms in it, ...

This is very common in Japanese:

1. build the noun phrase
2. attach は to make it the topic

So は is not marking just 天ぷら by itself in a simple way; it marks the whole phrase:

• きのこが入った天ぷら
  • は

軽くて is the -て form of the い-adjective 軽い.

• 軽い = light
• 軽くて = light, and...

The -て form links this description to the next part of the sentence.

So the structure is:

• 天ぷらは軽くて、祖父もおかわりしていました。
• The tempura was light, and Grandpa was also having seconds.

In food contexts, 軽い often means:

• not heavy
• not greasy
• easy to eat

So it is not necessarily about physical weight. It often describes a pleasant, not-too-rich texture or feeling.

祖父 is the speaker’s own grandfather in a neutral or somewhat formal way.

Japanese often distinguishes between:

• words used for your own family members when talking about them
• words used for someone else’s family members or when addressing them directly

So:

• 祖父 = my grandfather / our grandfather
• おじいさん = grandfather / old man, often used for someone else’s grandfather or as a more outward-facing term
• おじいちゃん = grandpa, more familiar/casual

In narration like this, 祖父 is very natural if the speaker is talking about their own grandfather.

も means also / too.

So 祖父も means:

• Grandpa too
• Grandpa also

This suggests someone else probably had another helping as well, or at least that Grandpa joined in.

It adds the nuance:

• not only others, but Grandpa as well

おかわり means another helping / a refill / seconds.

It combines with する:

• おかわりする = to have another helping / to ask for seconds

Then it becomes:

• おかわりしていました

This is していました, the past form of しています, built from する.

So grammatically:

• おかわりする → dictionary form
• おかわりしている → is having seconds / is in the state of getting another helping
• おかわりしていた / していました → was having seconds / was getting another helping

The お- in おかわり is part of the fixed word here. It does not necessarily make the sentence especially polite toward Grandpa; おかわり is simply the normal word.

していました gives a sense of an ongoing action or scene in the past, or it describes what was happening at that time.

So:

• おかわりしました = had another helping
• おかわりしていました = was having another helping / was getting seconds

In storytelling, 〜ていました often paints the scene more naturally, like describing what someone was doing.

Here it can suggest:

• Grandpa was in the middle of getting/eating another serving
• or, more loosely, Grandpa went back for seconds as part of the situation being described

So していました feels a little more descriptive and scene-setting than the simpler しました.