Is Genta also immortal? In episode 4, when the special forces infiltrated Rin's office, they shot Genta and he was obviously killed.

However, after that, when Mimi and Rin revived and returned to their office, Genta was seen alive again.

Does the forbidden fruit of immortality also apply for dogs as well?
Yes, Genta is immortal. As described on Wikipedia:


  Rin and Mimi's female dog who lives at their office. As an immortal, she does not age throughout the series and survives being shot on multiple occasions without any visible lasting injuries. Mimi takes her with her after the Asougi Consulting office is demolished in episode four. Genta is killed in episode five, leaving only ashes behind, just like human immortals whose time spores are removed.