Diga lo que diga mi hermano, ese personaje tiene más naturalidad que el héroe, y su historia no me produce tristeza, sino ganas de seguir leyendo.

This is a very common Spanish pattern:

diga lo que diga + subject

It means no matter what ... says or whatever ... says.

So:

• Diga lo que diga mi hermano = No matter what my brother says

The repetition is part of the structure. Literally, it is something like:

• Say what say my brother...

But in natural English, that becomes whatever my brother says or no matter what my brother says.

You will see the same pattern with other verbs too:

• Haga lo que haga = no matter what he/she does
• Vaya donde vaya = wherever he/she goes
• Sea como sea = however it may be / be that as it may

So the repetition is not accidental; it is a fixed concessive pattern.

No. Even though diga looks like the usted command form of decir, here it is not an imperative.

In this sentence, both instances of diga are part of a subjunctive concessive expression:

• Diga lo que diga mi hermano...

This means regardless of what my brother says...

A quick way to tell it is not a command is that the sentence would make no sense as an instruction. Nobody is being told to say something. Instead, the speaker is dismissing the importance of the brother’s opinion.

So here:

• diga = present subjunctive
• function = part of a fixed expression meaning no matter what

The subjunctive is used because the sentence expresses indefiniteness and concession.

The idea is not about one specific thing the brother says. It means:

• whatever he may say
• no matter what he says

Spanish very often uses the subjunctive in these kinds of broad, open-ended, indefinite expressions.

That is why you get:

• diga lo que diga
• haga lo que haga
• venga quien venga = no matter who comes
• pase lo que pase = whatever happens

If you used the indicative instead, it would lose that concessive whatever/no matter feeling.

Here lo que means something like what or whatever.

In the structure diga lo que diga, it helps form the meaning whatever he says.

A useful way to think of it:

• lo que = that which / what

Examples:

• No entiendo lo que dices = I don’t understand what you’re saying
• Haz lo que quieras = Do whatever you want

In your sentence, lo que is part of the repeated pattern and contributes to the idea of whatever:

• Diga lo que diga mi hermano = Whatever my brother says

Because the whole expression is built around diga lo que diga, and the subject can be placed afterward:

• Diga lo que diga mi hermano
• Mi hermano, diga lo que diga... would not mean the same thing

Spanish often allows the subject to appear after the verb, especially when the verbal structure is already clear.

So here the order is perfectly natural:

• diga lo que diga = fixed expression
• mi hermano = the person doing the saying

It is similar to English whatever my brother says, where my brother also comes after whatever.

This is about demonstratives:

• este = this
• ese = that
• aquel = that over there / that one further away

In modern Spanish, especially in many everyday contexts, the contrast between este and ese is often more about psychological or discourse distance than literal physical distance.

Here ese personaje means that character. It suggests the speaker is referring to a specific character already mentioned or clearly identifiable in context.

So:

• ese personaje = that character

Using este personaje would suggest a closer connection, as if the speaker were presenting or focusing more directly on the character as this character.

Both kinds of comparison are possible in Spanish, but they mean slightly different things.

Your sentence says:

• tiene más naturalidad que el héroe

Literally: has more naturalness than the hero

This compares the quality or degree of naturalness each character has.

If you said:

• es más natural que el héroe

that would mean:

• is more natural than the hero

That is also valid, but it describes the character directly with the adjective natural, rather than talking about the noun naturalidad.

So:

• tener más naturalidad = to have more naturalness, to come across more naturally
• ser más natural = to be more natural

The original version sounds a bit more literary or analytical.

Here naturalidad means something like:

• naturalness
• ease
• authenticity
• an unforced quality

When talking about a fictional character, tener naturalidad suggests the character feels believable, spontaneous, or lifelike.

So the speaker is saying that that character feels more convincing or more genuine than the hero.

It does not mean naturalness in a scientific or nature-related sense. It is about style, characterization, and emotional realism.

Because grammatical gender in Spanish is not determined only by the ending.

Héroe is a masculine noun:

• el héroe = the hero

Even though many masculine nouns end in -o, plenty of masculine nouns end in other letters:

• el hombre
• el padre
• el coche
• el héroe

The feminine counterpart is usually:

• la heroína = the heroine

So you simply need to learn héroe as a masculine noun.

Because sino is used after a negative statement to correct or replace what was just denied.

Structure:

• no X, sino Y = not X, but rather Y

So:

• no me produce tristeza, sino ganas de seguir leyendo
• it doesn’t make me feel sadness, but rather a desire to keep reading

This is different from pero, which is a more general but.

Compare:

• No es aburrido, sino interesante = It’s not boring, but rather interesting
• Es largo, pero interesante = It’s long, but interesting

In your sentence, the second part replaces the first, so sino is exactly the right word.

Spanish often leaves out the article with abstract nouns or general feelings, especially after certain verbs.

So:

• producir tristeza = to produce sadness
• tener ganas de... = to feel like / to want to...

Here:

• no me produce tristeza = it doesn’t cause me sadness
• sino ganas de seguir leyendo = but rather a desire / the urge to keep reading

Adding an article is possible in some contexts, but it would change the tone or sound less natural here.

For example:

• me produce tristeza sounds general and idiomatic
• me produce una tristeza enorme would be fine if you specify it more

And ganas is very often used without an article in this expression:

• tener ganas de comer
• dar ganas de reír
• me entran ganas de viajar

Me is the indirect object pronoun, meaning to me.

So:

• produce tristeza = causes sadness
• me produce tristeza = causes sadness to me / makes me feel sadness

In natural English, we would usually say:

• it doesn’t make me feel sad
• it doesn’t make me feel sadness

Spanish often uses this pattern:

• algo me produce + noun
• something causes me + feeling

Examples:

• Me produce miedo = It frightens me / It causes me fear
• Me produce alegría = It brings me joy
• Me produce tristeza = It causes me sadness

Because ganas is followed by de + infinitive when you say what someone feels like doing.

So:

• ganas de seguir leyendo = a desire to keep reading / the urge to keep reading

Breakdown:

• ganas de = desire to / urge to / feel like
• seguir = to continue, to keep on
• leyendo = reading

And seguir + gerundio is a very common structure meaning to keep doing something:

• seguir leyendo = keep reading
• seguir estudiando = keep studying
• seguir hablando = keep talking

So the whole phrase means the story makes the speaker want to continue reading.

Because after seguir, Spanish normally uses either:

1. an infinitive, when seguir means to continue with something

   • seguir leyendo is not this pattern

2. more commonly in this meaning, seguir + gerundio, meaning to keep doing something

   • seguir leyendo = to keep reading

So here leyendo is a gerund, like English reading in keep reading.

You cannot say:

• seguir leer ❌

The natural options are:

• seguir leyendo = keep reading
• continuar leyendo = continue reading

It can be ambiguous if you look at the words alone, because su can mean:

• his
• her
• its
• your (formal)
• their

But in context, su historia most likely refers to the story of that character or that character’s storyline.

Since the previous noun is ese personaje, English might translate it as:

• his story, if the character is male
• their story, if you want to stay neutral
• the character’s story, if you want to avoid ambiguity

Spanish often relies on context more than English does for possessives like su.

Because Diga lo que diga mi hermano is an introductory concessive clause.

It sets up the main statement:

• Diga lo que diga mi hermano, ese personaje tiene más naturalidad...

In English, you would also normally use a comma after an opening clause like:

• Whatever my brother says, that character...

So the comma helps separate:

1. the concessive opener: Diga lo que diga mi hermano
2. the main point: ese personaje tiene...

It sounds perfectly correct and natural, but somewhat careful or literary, especially because of expressions like:

• Diga lo que diga...
• tiene más naturalidad
• no me produce tristeza, sino ganas de seguir leyendo

In everyday conversation, someone might say something simpler, such as:

• Mi hermano diga lo que diga, ese personaje me parece más natural que el héroe.
• No me da tristeza su historia; me da ganas de seguir leyendo.

But the original sentence is not unnatural. It just sounds more polished, like something from a review, essay, or thoughtful conversation about a book.