The protagonist of Danganronpa 1 is called Makoto. But Joe streamed Danganronpa 1 after he'd already streamed Persona 5 which has a character called Makoto. After a character in Danganronpa used the phrase "Big Mac" to refer to Makoto, he decided to refer to the character as Big Mac too.[1]

Now he still sometimes refers to the protagonists of other games as Big Mac.

References

  1.     “Falco” video: “Joseph Anderson Danganronpa stream 4 with chat [07/20/2018” at 00:42:52].