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As Gustav finished squeezing every last drop of energy on him, he sighed on relief, resting over the grass as he saw the massive Inner World Develop even more, growing bigger and more massive than ever before…
"Hahh… It is done-"
"S-Sorry to interrupt you, Gustav, but now that you got the power, I recommend you assimilate Earth into your Inner World! There's enough leftover space for it to fit in!" said Gustav.
"Oh, right…"
Gustav still had yet to do something very important…
Save Earth!
He had indeed saved it already, he had done more than enough, in fact, but this wasn't enough for the great scheme of things! Earth would inevitably suffer yet another invasion. The fractures in space that let other dimensions breach with one another were not gone, Gaia had merely patched them temporarily, but like any patch, something from the other side could push forward and break it easily.
Check "The Protagnist's Sister Is Actually the Strongest"!