Atlan opened the door with the number '9' embossed on the metal. 9-star rarity Genus was the best anyone could ever hope for. But for Atlan, that was only second to the best. He had two 10-star Genus for himself that dictated his bloodline. Because of those two Genus, he became the Angelic Reaper of Souls.
He obtained the 10-star Grim Reaper Genus by stealing the God of Death's powers during his Pre-Remedium Draft while he got the 10-star Angel Genus by witnessing their global extinction from the face of the Earth.
If he obtained a 9-star Genus now, he didn't know if that would result in him changing his bloodline a third time. As far as he knew, only the strongest Genus could change his bloodline.
It doesn't matter. I'll probably gain another mutation from this Genus, and not a weak one at that.