From a distance, God’s wrath looks unfair. Why should people be punished for just not believing in Him? But this wrath, and the seven-plague judgement that goes with it, is for more than that. (The plagues could be literal or metaphorical, but that’s beside the point here.)
Two of the first three plagues are concerned with the sea and then freshwater turning to blood. The explanation for this series of disasters being not unfair is:
Revelation 14:5-6You are just, O Holy One, who is and who always was,
because you have sent these judgments.
Since they shed the blood
of your holy people and your prophets,
you have given them blood to drink.
It is their just reward.
The judgement that drives these plagues are further described as
Revelation 14:7Yes, O Lord God, the Almighty,
your judgments are true and just.
Do people have a chance to repent during this time? The answer appears to be ‘yes’, since there is a conflicting narrative in which people generally curse God for their condition rather than repent (so they must know He exists); yet there are some still watching for the Lord’s return, and they’ll be blessed.