Grycard System in the Apocalypse

https://www.webnovel.com/book/gricard-system-in-the-apocalypse_23996010206316105
Alex was still processing the fact that he had been reincarnated into another world in the body of a 15-year-old student, Agnus Vorhells, the youngest son of a baron, when an ethereal voice resounded through the heavens: [Mortals of Havengard, your sins have exceeded quota bearable by the Gods of the Eternal Void. Receive Divine Judgment].
Soon the skies shook with the roar of thunder and the black clouds turned day into night. The entire power system has collapsed. On land, accidents began to appear all over the city. In the skies, planes plummeted. The dead came back to life and began to devour the first person in sight.
As Havengard evolves with the arrival of the legendary mana, the now Agnus testified that the first kill would drop a spiritual book called Gricard, while the second kill onwards would drop a spirit card.
However, after he killed his first zombie, a cold voice echoed in the depths of his soul: [Ding!]
[The system has been assimilated with the host's soul successfully]
[Welcome to the Gricard System!]
[The host obtained the unique class, Arcane Thunder Reaper Mage]
[The system is opening the welcome pack...]
This is my first novel and my entry to the WPC #310.
Please I need honest opinions, even if it's critical.
Thanks!