Один персонаж выглядит виновным, хотя у него есть убедительное алиби.

It can do both.

In a sentence like Один персонаж..., один can mean:

• one character — literally one out of several
• a certain character — introducing one person in the story without naming them

So here it can sound like:

• One character looks guilty...
• or A certain character looks guilty...

That use of один is very common in Russian narratives.

Персонаж is grammatically masculine, regardless of the character’s actual gender.

Russian grammatical gender and real-life gender do not always match. So:

• персонаж = masculine noun
• therefore words agreeing with it also take masculine forms:
  • один
  • выглядит (singular verb form, same for all genders in the present)
  • виновным (masculine instrumental)

If you wanted to make the character explicitly female, Russian would often still keep персонаж masculine, because that is the noun’s grammatical gender.

Выглядит is the 3rd person singular of выглядеть.

Here it means:

• looks
• appears
• seems from the outside

So выглядит виновным means the character gives the impression of being guilty. It does not mean the person really is guilty.

That is important in this sentence, because the second part contrasts appearance with evidence:

• he looks guilty
• but he has a convincing alibi

Because after выглядеть Russian often uses the instrumental case for the word describing how someone appears.

So:

• виновный = nominative form
• виновным = instrumental singular masculine

This pattern is very common:

• Он выглядит уставшим. = He looks tired.
• Она выглядит счастливой. = She looks happy.
• Персонаж выглядит виновным. = The character looks guilty.

So the instrumental here marks the state or quality that someone seems to have.

Yes.

Both are possible, but the nuance is a little different:

• виновным = guilty, culpable; a bit more formal or objective-sounding
• виноватым = guilty-looking / as if feeling at fault; often a bit more everyday or emotional

In many contexts they are close. In a detective-story type sentence, виновным works well because it fits the idea of actual guilt versus innocence.

Хотя means although, though, or even though.

It introduces a clause that contrasts with the first one:

• Один персонаж выглядит виновным
• хотя у него есть убедительное алиби

So the structure is:

• X seems true
• although Y suggests the opposite

This is a very common Russian conjunction for contrast.

Because Russian usually expresses possession with the pattern:

• у + genitive + есть

Literally, it is something like:

• at him there is

So:

• у него есть алиби = he has an alibi

This is much more natural in ordinary Russian than using иметь.

Russian does have иметь = to have, but it is often:

• more formal
• more abstract
• less common in everyday possession statements

So у него есть алиби is exactly the normal way to say it.

Because у requires the genitive case.

The pronoun он changes like this:

• nominative: он
• genitive: его

But after many prepositions, Russian adds н- to third-person pronouns:

• у него
• с ним
• к ней
• от них

So here:

• у него = by him / at his place / in his possession

That is just the normal prepositional form.

Good question. Russian often omits the present tense to be, but есть is still commonly used in existence/possession constructions.

Compare:

• Он врач. = He is a doctor.
  No есть.

But:

• У него есть алиби. = He has an alibi.
  Есть is natural here.

In this kind of sentence, есть emphasizes that something exists or is available. So it is perfectly normal.

Without есть, у него алиби is possible in some contexts, but у него есть алиби is the standard neutral phrasing.

That is right: алиби is an indeclinable noun, so its form usually stays the same.

However, it still has grammatical properties. In modern Russian, алиби is normally treated as neuter.

So the adjective must agree with it:

• убедительное = neuter singular
• алиби = indeclinable neuter noun

That is why you get:

• убедительное алиби = a convincing alibi

Even though алиби itself does not change form, words modifying it still show agreement.

In у него есть убедительное алиби, алиби is in the nominative case, because it is the thing that exists in the possession construction.

So the structure is basically:

• у него = with him / in his possession
• есть = there is
• убедительное алиби = a convincing alibi

Since алиби is indeclinable, its form looks the same in different cases, but functionally here it is nominative.

The given word order is natural and neutral, but Russian word order is flexible.

Neutral version:

• Один персонаж выглядит виновным, хотя у него есть убедительное алиби.

You could also rearrange parts for emphasis, for example:

• Хотя у него есть убедительное алиби, один персонаж выглядит виновным.

That puts more focus on the contrast from the start: although he has a convincing alibi...

So the meaning stays the same, but the emphasis changes.