Let's begin with understanding the actual issue itself.

In P4AU's PC port, analog input detection is shoddy, and makes playing using an analog stick near unplayable.

To put it bluntly, The game will almost always input diagonal directions over cardinal directions, which can only be input with exact angles.

First, Controller Configuration needs to be enabled.

• In Steam click on the Steam menu tab, and select Settings.
  
  
• Select Controller in the pop-up window, and click on General Controller Settings.
  
  
• Enable support for your controller type. Alternatively, check every box in order to make sure your controller is supported.
  
  
• Finally, restart steam to ensure that changes to settings take effect.

Next, open the controller configuration menu. This can be done in 3 ways:

• On the P4AU tab in the Library, click on the Gear icon. From there, select Manage->Controller configuration.
  
  
• While P4AU is open, enter the Steam Overlay with Shift + Tab.From there, click on Controller configuration in the top right corner.
  
  
• In Big Picture Mode, select Controller Configuration under P4AU's Manage Game menu.
  

NOTE: Your controller needs to be turned on in order for the menu to be accessible.

Change the Left Control Stick to a Directional Pad with 8-Way Input, using the controller's D-Pad as each direction.
Set the Overlap Region to what best suits you. This is what dictates how far you need to move the stick to set a diagonal. For reference, P4AU's default analog conversion essentially has a maxed out Overlap region, meaning that almost the entire range of the stick is on Diagonal inputs. Somewhere in the middle is a good place to start while tweaking it.


And that should be it! Analog input (should) be more bearable now!