Chapter 652: Grandpa got OP
Rei was an AI Robot invented by Byakuya Ishigami, Senku's father. This was a project Byakuya had worked on for a long time and Senku had seen it too. It was present during the petrification event and made its debut to the astronaut crew soon after, revealing itself as version 37, a much more rounder and slicker version. It was later revealed that while Rei had the brain-power of 60 smartphone boards and was filled with useful scientific knowledge, it lacked common-sense protocols and human biology information, such as average human life spans.
Rei was pivotal in returning the astronauts to earth, providing the necessary scientific data and doing all the necessary calculations and simulations in order for the Souyz Module to land safely in an appropriate position. Before they all left Rei, Byakuya, with a sorrowful expression, told Rei that it is his friend and he will one day return for it.
Byakuya's promise was actually a lie. The astronauts needed all of the station's fuel to go back down on earth, and the International Space Station would, on its own, burn into the earth's atmosphere in about a year from the current date. Byakuya knew all that and never intended to come back for Rei. The promise was intended for the little robot to pass on in peace.
Rei instead took Byakuya's promise literally and took it upon itself to maintain and keep the ISS in orbit until Byakuya's return. To that end, it modified itself to first fix the solar panels by attaching itself to the space station's arms. When it found out that the astronauts used all of the station's fuel, it found a way to modify the food they left behind into fossil fuel to return the ISS back into its original orbit. And when that ran out, it modified the station's engine to be hydrogen-powered.
At some point, Rei discovers that there was something wrong with its brain. Of the 60 smartphone boards inside it, 12 had ceased functioning. This was because the high energy particles coming out of the sun can burn delicate circuitry. Not to be one to give up, it used the station's computer circuits to upgrade its brain with the capabilities of 1'000 SP (smartphone points) to match up to its upgraded functionality.
20 years after the petrification event,
~I wonder how Byakuya is doing.~ Rei wondered
For the next few years, Rei kept on fixing the ISS and also itself by going out for resource hinting. He found all the remaining satellites and used them.
42 years after the petrification event, Rei realised that Byakuya must not know it was still OK and in space, so it decided to make a light signal to show Byakuya where it was in order to him to return. Unfortunately, it was too late.