Thanks for the chapter and for translating the whole manga.
Well, this story certainly was something. A better wish would have probably been to create a device that makes it so the Cube and the reason behinds its creation were never there in the first place, undoing 28 chapters worth of drama, frustration and tears.
The manga tried to ask philosophical questions and this scenario would surely be pretty interesting, but it all falls flat in the end. For the main character to not have a problem with killing billions for rather simple things is the definition of insanity and inhumanity. Even worse when the story wants to portray him as the best optimal choice the Cube could have taken because of his lack of ideology (whereas in different beliefs would even favor dying in the worlds stead).
His time outside the cube was every plot twist happening left and right, good guys being bad then good then bad then etc. which didn't make the read better. The antagonist at the end with his random power up, constant ramblings about god (he says gods sometimes, so which one is it) and his goals (at the end he wants to portray himself as a saviour but then not) were also written incoherently.
Everything condensed, this manga really lacks an idea of what it wants to be; what its characters should be. Do we want a calculating MC who only things about himself? Oh, how about an edgy teen? No, lets go back to calculating and manipulative. Scratch that, he was actually good the whole time and can't continue to live at the end because of his conscience. Oh btw, he good a girlfriend, who is a normal school girl, wants to have sex with him, but a psycho aaaaand she can make a small satelite and....
The list goes on.
I just noticed it now, but the artist Okazaki Kei also drew "Haiyore! Nyaruko-san". What a coincidence (and sad that it only has two translated chapters in english, I quite liked Nyaruko in their artstyle)