Этот персонаж остался моим любимым не потому, что он был прав, а потому, что он честно искал правду.

Because after остаться / остаться кем? чем? Russian often uses the instrumental case for a noun or adjective that describes what someone or something remained.

So:

• остался моим любимым = remained my favorite
• literally: remained as my favorite

This is a common pattern:

• Он остался другом. = He remained a friend.
• Она осталась спокойной. = She remained calm.

Here, любимым agrees with персонаж and therefore is masculine singular instrumental, and моим matches it.

Because любимый is not acting like a normal subject here. It is part of the predicate after остался, so it takes the instrumental:

• nominative: любимый
• instrumental: любимым

Also, мой любимый is being used almost like a noun: my favorite one / my favorite character. Russian often does this with adjectives.

So:

• Этот персонаж — мой любимый. = This character is my favorite.
• Этот персонаж остался моим любимым. = This character remained my favorite.

The second sentence uses instrumental because of остался.

Остался is the past tense, masculine singular form of остаться, which usually means to remain, to stay, or to be left.

In this sentence it means:

• This character remained my favorite

The form is masculine singular because персонаж is masculine singular.

Related forms:

• он остался
• она осталась
• оно осталось
• они остались

Because остался means remained, not became.

• стал = became
• остался = remained

So the sentence is saying that the character continued to be the speaker’s favorite, not that he became the favorite for the first time.

Compare:

• Он стал моим любимым персонажем. = He became my favorite character.
• Он остался моим любимым. = He remained my favorite.

That difference is important here.

This is a very common Russian pattern meaning:

• not because ..., but because ...

So:

• не потому, что он был прав
• а потому, что он честно искал правду

= not because he was right, but because he honestly searched for the truth

A few things to notice:

1. потому, что introduces a reason.
2. не потому, что ... rejects one reason.
3. а потому, что ... gives the real reason.
4. а here means but, in a contrastive sense.

This whole structure is extremely useful in Russian.

Example:

• Я пришёл не потому, что должен был, а потому, что хотел.
• I came not because I had to, but because I wanted to.

Because что introduces a subordinate clause.

Russian punctuation is stricter than English in this area: when a clause introduced by что appears, it is normally separated by a comma.

So:

• не потому, что он был прав
• а потому, что он честно искал правду

Each что starts a clause with its own subject and verb:

• он был прав
• он честно искал правду

That is why the commas are required.

Because прав here is the short form of the adjective правый / прав in the sense of being right, correct.

In Russian, прав is the normal predicative form used for saying someone is right:

• Я прав. = I am right.
• Ты прав. = You are right.
• Она права. = She is right.
• Они правы. = They are right.

So:

• он был прав = he was right

Do not use правый here. Правый usually means right-hand, right-side, or in some contexts right-wing.

And правым would not fit this structure.

Because the sentence focuses on the process of searching, not on a completed result.

• искать = imperfective, to search / to be searching / to seek
• найти = perfective, to find

So:

• он честно искал правду = he honestly sought the truth
• not necessarily he found it

This choice is very meaningful. The sentence praises the character not for already possessing the truth, but for sincerely trying to find it.

If you changed it to a perfective verb, the meaning would shift toward completion or result.

They come from different words and mean different things.

• прав = right / correct
• правда = truth

In the sentence:

• он был прав = he was right
• искал правду = he was searching for the truth

Правду is the accusative singular of правда, because it is the direct object of искал.

So even though the words are related historically and semantically, they are doing completely different jobs here.

Because искать usually takes a direct object in the accusative.

So:

• искать кого? что?
• искать правду

Examples:

• искать ответ = to look for an answer
• искать выход = to look for a way out
• искать правду = to seek the truth

Since правда is a feminine noun ending in -а, its accusative singular form is правду.

Честно means honestly.

It is an adverb because it modifies the verb искал:

• искал как? — честно
• searched how? — honestly

So the sentence means that he searched in a sincere, honest way.

Compare:

• честный человек = an honest person
  here честный is an adjective
• он честно искал = he honestly searched
  here честно is an adverb

Because each что introduces its own subordinate clause, and each clause has its own subject:

• что он был прав
• что он честно искал правду

In English, repetition can sometimes be reduced more freely, but in Russian it is very normal and natural to repeat the subject in each clause.

This makes the structure clear and balanced, especially in a contrast like:

• not because he was right
• but because he honestly sought the truth

Yes, essentially.

Russian often allows an adjective to stand on its own when the noun is obvious from context.

So:

• моим любимым here means something like my favorite one / my favorite character

The full version could be:

• Этот персонаж остался моим любимым персонажем.

But that sounds repetitive because персонаж has already been mentioned. Russian prefers the shorter version here.

Because that is the topic: the sentence is about this character.

Russian word order is flexible, but the beginning of the sentence often presents the topic or what the speaker wants to focus on first.

So:

• Этот персонаж остался моим любимым...

naturally means something like:

• As for this character, he remained my favorite...

The sentence then explains why.

Not naturally in this sentence.

Although любимый can mean beloved, here мой любимый is the very common way to say my favorite.

So:

• мой любимый фильм = my favorite film
• мой любимый герой = my favorite hero
• остался моим любимым = remained my favorite

Using beloved in English here would sound too emotional or literary unless that tone was intended.

The sentence contrasts being correct with searching sincerely for truth.

So the speaker is saying:

• the character is not a favorite because he always had the right answer,
• but because he made an honest effort to find the truth.

That gives the sentence a thoughtful, morally reflective tone. It values integrity and sincerity more than simply being right.