Asetoni FFXV | FFXV greatsword moveset @asetoniffxv22 | Uploaded November 2016 | Updated October 2024, 2 hours ago.
If you wanna know more about the forward+O combo then click here: youtube.com/watch?v=GiNeP1EFq4s

This is how you do different attacks in FFXV:

Even though you only have one attack button, O, you can do a variety of different moves by pushing the left analog stick in different directions while attacking. Also, releasing and re-pressing O can also trigger certain attacks. Other factors, such as distance to the enemy can also cause different moves to happen.

Most weapons have 5 different ground attacks and one aerial attack or combo. The ground attacks usually are:

Basic combo (just hold O)
Left analog stick forward + O
Left analog stick backwards + O
Left analog stick to either side + O
Stop holding O during a combo and re-press it after a split second.

A GameFAQs thread where I explain the movesets of all weapons:
gamefaqs.com/boards/932981-final-fantasy-xv/74560055