In the timeline: July 5th. Post Rise dungeon. Will rain in three days from now.
About 12 years before the events of Persona 3 and 4 (back in 1999), the Kirijo Group decided that building robots designed to fight Shadows was a great idea. So they made a prototype that worked awesomely so they built more.
Most of the Androids made had a female appearance. The others were male so to speak.
And one of the 'male' bots was given the name Souji. Unfortunately for Souji, in his first training exercise, he failed to summon his Persona. He was put offline after repeated failures. He would've been scrapped but one scientist thought that he could figure out what went wrong and spent awhile writing new code in his appartment where he hid Souji for the next ten and half years. Meanwhile, Aigis was the only one left intact after fighting the Death Arcana Shadow and was left in stasis (or something) in Yakushima.
After the plot of Persona 3 occured, Aigis mentions having a 'younger brother' who 'went away' after he kept epic failing at being an Anti-Shadow weapon. Mitsuru asks around to see what happened to him and learns that despite being told to scrap him, the scientist keeping Souji still has him and has been writing new code/software that would make him more lifelike and could easily pass off as human. Intrigued, Aigis asks if she can have that upgrade after being introduced to a rewakened Souji who for some reason still has the anti-Shadow program installed.
However, even though Souji appears human and can show emotions and empathy, he still has a lot to learn about people. And then there is the fact that he still can't summon a Persona.
Souji's 'father' then one day gets married only to discover a few months later that his new wife is on the run from some Yakuza who she borrowed a very large loan from once. To protect Souji, Mitsuru suggests that he should be separated from his 'parents' until the matter is solved. Souji is informed that he is going to be sent to Inaba where his 'uncle' (brother of the new wife) lives. There he'll continue to learn about being human by interacting with the locals.
Of course, when he got there, he shakes hands with a gas station attendent that causes a small error to occur and made him 'feel' ill. However, he shrugs this off as a coincidence.
And then the plot happens. To Souji's relief, he can finally summon a Persona. To his surprise later, he discovers he can weild multiple Personae.
But will his stay in Inaba help him understand humans? Will he solve the murder case? Etc. Etc.?
Other info:
-As of July, nobody realizes what Souji really is (except maybe Dojima)
-He's most likely not going to have a girlfriend/boyfriend during his stay
-He'll also epic fail at flirting
-He's not based on the
Sexbot!Souji fic on the kink meme. Rly.
Even though it was me who requested that.-He has dissuaded Aigis from rushing over to Inaba whenever they contact each other. He's not going to tell her about what really happened in the Strip Club (ie, everyone would've died if it weren't for Teddie).
-He'll automatically greet any Aigis he sees and might refer to her as 'sister'
-Aigis secretly plans on visiting Souji in Inaba. This will happen in late October.
-The official alibi in why he's in Inaba is because his 'parents' are working overseas and...yeah, it will take about a year for his 'parents' to fix that loan issue. :/
-He still fights using a sword.
-He knows what Teddie is from the start. By mid-June, he started to trust him more and was surprised that the Bear saved everyone from Shadow!Rise at the risk of his own life and gained a Shadow and a Persona in the process. That was two days ago.