Moj unuk se više ne boji mraka.

Moj is the masculine singular nominative form of the possessive adjective meaning my.

It matches unuk because:

• unuk = grandson
• it is masculine
• it is singular
• it is the subject of the sentence, so it is in the nominative

So:

• moj unuk = my grandson

If the noun changed, moj would change too:

• moja unuka = my granddaughter
• moje dijete = my child

Se is a reflexive clitic, and it is part of the verb expression bojati se, which means to be afraid.

So the verb is not just bojati. The normal form is:

• bojati se = to fear / to be afraid

That means:

• bojim se = I am afraid
• boji se = he/she is afraid
• ne bojim se = I am not afraid

In this sentence:

• Moj unuk se ... boji = My grandson ... is afraid

Even though se may look like himself/herself, here it is simply part of the verb and usually is not translated separately.

Boji is the 3rd person singular present tense form of bojati se.

It agrees with moj unuk because my grandson = he.

Present tense forms of bojati se are:

• ja se bojim = I am afraid
• ti se bojiš = you are afraid
• on/ona se boji = he/she is afraid
• mi se bojimo = we are afraid
• vi se bojite = you are afraid
• oni/one se boje = they are afraid

So:

• moj unuk ... boji se -> he is afraid

Together, više ne means no longer or not anymore.

So:

• ne boji se = he is not afraid
• više se ne boji / se više ne boji = he is no longer afraid

Here više does not mean more in the usual comparative sense. In this pattern, it means something like any longer.

Examples:

• Više ne radim tamo. = I no longer work there.
• On više ne puši. = He doesn’t smoke anymore.

So in your sentence:

• Moj unuk se više ne boji mraka. = My grandson is no longer afraid of the dark.

Because bojati se requires the genitive case.

The noun mrak normally appears as:

• mrak = nominative singular

But after bojati se, it changes to genitive:

• mraka = genitive singular

So:

• bojati se mraka = to be afraid of the dark

This is something learners usually just have to remember with the verb:

• bojati se + genitive

More examples:

• bojim se psa = I’m afraid of the dog
• boji se vode = he/she is afraid of water
• boje se visine = they are afraid of heights

In this sentence, mraka is most naturally understood as the dark.

The noun mrak literally means darkness, but in everyday English the best translation here is usually:

• bojati se mraka = to be afraid of the dark

That is the natural idiomatic equivalent.

Yes, Croatian word order is fairly flexible, but clitics like se usually come near the beginning of the clause, often in the second position.

So this sentence:

• Moj unuk se više ne boji mraka.

is very natural.

You may also hear:

• Moj unuk više se ne boji mraka.
• Moj unuk više ne boji se mraka. — much less natural
• Više se moj unuk ne boji mraka. — possible, but marked for emphasis

The most neutral version is the original one.

A useful rule for learners:

• clitics like se and short forms often come early in the sentence
• Croatian allows movement for emphasis, but not every order sounds equally natural

That order is possible in some contexts, but it is less neutral and less standard-sounding for everyday use.

In Croatian, short unstressed words such as se usually prefer an early clitic position. So the most natural order is:

• Moj unuk se ne boji mraka.
• Moj unuk se više ne boji mraka.

Putting ne before the main verb is required, but se often stays earlier in the clitic slot rather than directly after ne.

So learners should usually model sentences like this:

• On se boji.
• On se ne boji.
• On se više ne boji.

Yes, boji se is present tense.

Croatian often uses the present tense to describe a current state:

• boji se = he is afraid

English does the same, but the natural translation includes is because English says:

• he is afraid not
• he fears in most everyday situations

So:

• Moj unuk se više ne boji mraka. literally resembles:
• My grandson no longer fears the dark

But the most natural English is:

• My grandson is no longer afraid of the dark.

The dictionary form is bojati se.

When learning Croatian verbs, it is important to learn some verbs together with their reflexive particle or required case pattern.

So it is better to memorize:

• bojati se + genitive

not just:

• bojati

That helps you produce correct phrases like:

• bojim se mraka
• bojiš se pasa
• boje se promjene

Grammatically, yes. But it changes the meaning.

• Moj unuk = my grandson
• Unuk = a grandson / the grandson, depending on context

Croatian often leaves out possessives when they are obvious from context, but if you specifically want to say my grandson, you should keep moj.

So:

• Moj unuk se više ne boji mraka. = My grandson is no longer afraid of the dark.
• Unuk se više ne boji mraka. = The grandson / a grandson is no longer afraid of the dark.

Usually it appears before the main verb idea, but because of clitics, the exact placement can look a little different.

For example:

• On više ne radi. = He no longer works.
• Ona se više ne boji. = She is no longer afraid.
• Mi više ne možemo čekati. = We can no longer wait.

With reflexive verbs, se often comes before više ne or near them:

• On se više ne boji.
• Ona se više ne smije toga.

So the important thing to recognize is the unit of meaning:

• više ne = no longer / not anymore

Even if a clitic like se appears nearby, the meaning remains the same.