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Since the moment he meet Verde that his life slowly changed, as he lived many new experiences, and ultimately managed to reach an understanding with his father that he would take care of the eggs and would rise them and show him that dragons raised with care could still be strong.
Like this, he raised a whole clutch of eggs from there, and the weakest and smallest yet the most adventurous and brave of them all was Ignatius, whom Agni day after day troubled himself in raising due to all he little shenanigans that the dragon made.
I can see why he loves the little Ignatius so much; he has been his most protected one. And he raised him with lots of care so he could become decently strong to be recognized by their father. But at the end, when Ignatius heard about the Heroes finally ending the demon war, he thought they were a fitting challenge for someone like him and recklessly flew to the continent of Cloudia, meeting his end.
Check "The Protagnist's Sister Is Actually the Strongest"!