Generally macros/scripts/turbo are banned in speedrunning. However in DMC1 Dante Must Die, usage of turbo is allowed. This because of excessive shooting section. Most notable ones are Mission 1 Griffon 2 and Mundus Turbo is a feature that allows for one button press to do a repeated amount of actions. In other words, pressing or holding down the button that is activated under Turbo Mode, allows for the button to replicate pressing the same button over and over. On paper, it is possible to get max shooting speed on keyboard because a keyboard will actually let you mash the correct way to obtain the speed. Although, it's hard to maintain the consistency while performing other actions or playing the game in a long session.
Follow Waifu's tutorial first before the macro setup.
Once you save and apply the changes from steam Big Picture download Auto Hot Key along with this script to set up Mundus 1 fight for Max Shotting speed on your J key. After you install the software, you only need to run the script. You should find H icon on your taskbar, which you can exit and stop the turbo key after you finish your session.
In general, you will have to buy third party controller that provides turbo function. Usually Hori and 8BitDo products are the most reliable in terms of quality. On the Other hand, PS4 users have the cheapest option with Back Button Attachment. Some good examples:
