The main character with high intellect and a photographic memory. He wants to be an astronomer who works at NASA due to a promise he made with his childhood friend Kuroneko. After meeting the magic users, he decides to provide shelter to them at an abandoned observatory despite knowing that their pursuers have orders to kill whoever comes in contact with them, usually coming with plans to have their location concealed while looking for ways to provide the medicine they need to keep living while helping them to live their lives as normal as possible.

Later in the manga, it was revealed by Nanami that when Ryouta and Neko went to the dam and fell down, Neko dies but was revived in the lab which gave her magic powers but lost her memories upto that point. Ryouta's body was beyond saving, so they reconstructed his body and put his memories in it. Due to the reconstruction he gains photographic memories power.

Nanami also reveals that he will soon die due to having photographic memory power because his brain's memories is nearly fully filled and soon his brain will overload and suspend activities which means it will die, Unless Nanami erases herself from Ryouta's memories which will result in him saving but completely forgetting Nanami's existence.
(Source: Wikipedia)