Reverse Diode and Resistor in parallel for battery connection. What do they do?
This is called a power-on reset. When power first comes on, charge flows through R14 to slowly charge C5. While this is going on, whatever is connected to the HARD-RESET line will be held in reset until the voltage passes the threshold from logical '0' to '1'.

When power is cut off, D1 quickly drains C5 so that the reset line functions correctly for any subsequent power-on.

You want a power-on reset so that everything gets set to a known state when you first apply power.