Both are by the same writer. School theme, strong female lead who cares about her friends so much, wonderful male lead, adorable romance. Both deal with many social issues that students experience in school. They also address corruption in private schools. Sassy Go Go can be triggering with some suicidal behaviour and both can be triggering with violence.
Both of them have a similar feel. D-Day is a medical drama based on a natural disaster but there's an entire storyline about the firefighters. Love 911 has more comedy but also has its fair share of drama. In both the female lead is a doctors. In D-Day the male lead is a doctor whereas in Love 911 he's a firefighter. Both are satisfying with the romance.
They both have a similar story. In both the male lead has an argument with their parent and gets sent back in time to the year before they were born to get to know their parent and understand why their parent made certain choices. In both the male lead finds love along the way.