Soon after Future Hiiro defeated the Demon Nanatsubaki in the Past, he was forcibly moved back to the future, but due to her resistance, there was something akin to a pit stop during his young days, soon after the above arrangement was made.
As he left the building, he saved a street bum girl, who was revealed to be Snow, and to protect her, he sent her to Rei, who at the time, well, you can read the initial chapters to see her impressions of Hiiro. Hence, treating Snow as a Mob is correct, she was not a character in the game, and only exists because this Hiiro changed the past.
To definitively defeat Nanatsubaki, and considering he had limited time in this period, he had to meet the Margelines, and prepare them to the future battle, there he accidentally met with young Ophelia, who fell in love with him, mistaking him for a girl (because he was dressed as a girl). Ophelia mistook his name "Hiiro" for "Hiro"
Hiiro gives her an item (the key to Nanatsubaki's defeat), telling her to keep it safe, and also giving her some messages for his future self (And he did get the messages before traveling to the past). He then is able to confirm things with Ophelia's older sister, and soon after, he returns to the present.
He did mention everyone to not contact him and treat him as an unknown person, because once his future self returns, the "he" that remains won't remember anything.