After the End: Serenity
Theoretically, reaching the point where no one could progress was impossible.
Unfortunately, the theory was wrong. Everything reached a point of stasis. Stars still burned and worlds still rotated around them, but no intelligent beings strove to excel - or even to survive.
Except one - and all he did was exist. There was no reason for him to do more.
Eventually, Order’s Voice found a way out. If the only existing being would agree to give up most of his power, the Voice could reset the multiverse to an earlier time. Of course, the Voice couldn't ask it that way. It could only ask if the Last Reaper was willing to start over from when Earth was first brought into Order.
There were many things - many abilities - that were simply too much a part of the Last Reaper to be removed from him, even sent back in time. Order's Voice was not made to remove ability, after all. It wouldn’t be fitting to have the Voice's greatest success die from too much power for his mortal body to handle, so he needed a stronger body. If he truly objected, well, the Voice would leave a way out. Not that the Voice was going to tell the Last Reaper anything about it. That would be pointless - and impossible.
When he landed in his old body - more or less - on Earth, the Last Reaper once again became Thomas. He was both and neither. He needed a new name for a new life, and the Tutorial was the perfect place for a new name.
A note on the nonhuman lead tag: He isn't human, and hasn't been human for a very, very long time (or maybe not long at all, depending on how you count it). He still thinks of himself as human, either way.
The cover image is a Chandra/Hubble composite image of VV 340 / Arp 302 / UGC 9618. While we're not going to space any time soon in the story, people from elsewhere are coming to Earth - so it seemed appropriate. Plus, I like space imagery.