All right, time for new speculations:
1. The uncle did NOT set the fire but knows who did it and is keeping quiet in case the REAL killer comes after Nanaka.
2. The REAL killer is the old lady in the home, who will come after Nanaka anyway. (she a real psycho btw)
3. Grandma will come after Nanaka with a chopper while all bloody, forcing Sana to overcome his fear of blood to save Nanaka.
4. In the process get stuck in a fire (sets by old lady, meant for Nanaka) forcing Nanaka to overcome the pyro-phobia to save Sana.
5. Motive for old lady is Nanaka's violin. She's a better player than her grandkid so she did it to kill off the competition. Ironically. the whole family got killed while traveling to a violin competition so she's somewhat responsible to the deaths..
....Or maybe not
