Learn Hardcore Japanese: tomodati ga sono aikon wo mite, 「kirei da ne」 to komento wo site kuremasita. - A friend saw that icon and kindly left the comment, “It’s beautiful.”

が marks 友達 as the grammatical subject doing the action (seeing and commenting).
In this sentence, we’re simply reporting what the friend did, so 友達が is natural.

You could say 友達はそのアイコンを見て…, but it slightly shifts the nuance:

友達が… = “My friend (the one who did it) saw it and commented…”
友達は… = “As for my friend, (he/she) saw it and commented…” – it feels a bit more like you’re contrasting your friend with someone else or introducing a topic you’ll talk more about.

In isolation, 友達が is the more neutral, straightforward choice here.

What is the role of その before アイコン? Why not just アイコン?

その means “that (one)” and usually refers to something that both speaker and listener already know or that has been mentioned before.
So そのアイコン implies “that icon (we both know which one)” – maybe a profile picture you were just talking about.

If you just said アイコン, it would be more like “an icon” or “the icon” with no explicit signal that it’s already shared knowledge.
You use その to anchor it to the shared context.

What does the て-form in 見て do here? Does it mean “and” or “after”?

The て-form (here, 見て) is connecting two actions done by the same subject (the friend):

そのアイコンを見て、コメントをしてくれました。

This can be understood as:

“(He/She) saw the icon and then commented,” or
“After seeing the icon, (he/she) commented.”

Japanese doesn’t clearly separate “and” vs “after” here; it just shows that seeing happened and then commenting happened, in that order.
Context fills in the nuance of sequence.

What does と do after きれいだね? Why is it needed?

と here is the quotative particle. It marks the content of what was said or thought.

「きれいだね」とコメントをしてくれました。
= “(My friend) commented ‘It’s pretty, isn’t it?’”

In English, we use quotation marks or that-clauses. In Japanese, と plays that role: it attaches the quote (きれいだね) to the verb of saying/thinking (コメントをする, 言う, 思う, etc.).
Without と, you can’t clearly mark that きれいだね is what was said.

Why do we have both 「きれいだね」と and コメントをして? Isn’t that redundant?

They have different roles:

「きれいだね」と = marks the content of the speech (what was said).
コメントをして = describes the action (“made a comment”).

Together they mean “(my friend) commented, saying ‘It’s pretty, isn’t it?’.”
You could also say 「きれいだね」と言ってくれました, where 言って is “said.”
So it’s not redundant; と links the words to the speech verb, and コメントをして is that speech/action verb.

Why is it コメントをして and not just コメントして? Is the を necessary?

コメントする is a サ変動詞 (noun + する verb). With these, を is often optional in everyday speech:

コメントをする and コメントする both mean “to comment.”

So:

コメントをしてくれました
コメントしてくれました

are both grammatically fine.
Including を can feel a bit more careful or explicit; dropping it sounds slightly more casual and is very common in conversation.

Why use コメントする instead of 言う? Could I say 「きれいだね」と言ってくれました?

Yes, 「きれいだね」と言ってくれました is perfectly correct and natural.

Nuance:

コメントする – “to comment,” often used for posts, SNS, online comments, or “leaving a comment” on something.
言う – “to say,” the general verb for saying something.

In a context like social media, コメントする nicely matches the idea of “left a comment on it.”
In an ordinary face‑to‑face conversation, 言う might be slightly more neutral. Both are fine; context decides which feels more natural.

In きれいだね, why do we need だ? Could it just be きれいね?

きれい is a な‑adjective, which normally needs だ (or another copula form) to make a full statement:

きれいだ。 = “It’s pretty.”

In casual speech, people sometimes say きれいね without だ, and that is also used, but:

きれいだね is very standard and neutral casual/polite-mixed speech.
きれいね can sound a bit more feminine or old-fashioned in some contexts, depending on tone and region.

So きれいだね is a safe, common way to say “It’s pretty, isn’t it?”

What is the nuance of ね at the end of きれいだね?

ね softens the statement and seeks agreement or shared feeling.
So きれいだね is like:

“It’s pretty, isn’t it?”
“It’s pretty, right?”
“It’s so pretty, huh.”

Without ね, きれいだ is a plain assertion and can sound blunt in conversation.
Adding ね makes it friendly and inclusive, as if inviting the listener to agree.

What exactly does くれました add? Why not just コメントをしました?

くれる is a benefactive verb: it means someone does something for me / for us (the speaker’s side).

コメントをしました。 = “(They) commented.” (neutral fact)
コメントをしてくれました。 = “(They) kindly commented for me / on my behalf, and I feel grateful.”

So 〜てくれる expresses that the action was beneficial to the speaker and often carries a nuance of appreciation.
In English we don’t have a direct equivalent, but you can feel it as “did (me) the favor of commenting.”

Can I replace くれました with くれた? What changes?

Yes:

コメントをしてくれました。 – polite past.
コメントをしてくれた。 – casual past.

The meaning is the same (friend did the favor of commenting), but くれました is polite, suitable for talking to someone you’re not very close to or in a formal setting.
くれた is what you’d say to friends, family, etc., in casual conversation.

There are two を in the sentence (アイコンを, コメントを). Is that okay in Japanese?

Yes, that’s fine. Each を belongs to a different verb phrase:

そのアイコンを見て – “(my friend) saw that icon”
コメントをしてくれました – “(my friend) made a comment (for me)”

They are separated by the て-form (見て) which links the two actions.
Japanese allows multiple を in one sentence as long as each clearly attaches to its own verb.