Its the same story but i think the old chapters are like oneshot only and the whole manga got serialized so they changed chapter 1 and 2
the likely reason for the change in her name was that her LEGAL guardian had changed since it is more often than not SIMPLER for the child to take the last name of who ever is watching over them while their parent is abroad or working long distances from the home . my ex wife and i had a few issues while we were living in Japan our daughter has my last name but looks just like her mother Japanese unlike me i am Native American Apache and Northern European and picking up my daughter some days like at the beginning of the school year was a MASSIVE pain in the ass because not only did they want my ID but my passport and all kinds of stupid shit at first all due to my daughters last name and her looks
I dont know why Touko's name was changed. In the first chapter her name was Narumi Touko while on the contact saved it was Mamiya, are they written the same in japanese? (〜￣△￣)〜