Might be old news to some of you, but bear with me. The greatsword is slow and powerful, yes? I use it quite a lot, and when fighting things like Vdrome, Gdrome, and Idrome, there's nothing more annoying than lining up a swing and having the damn thing jump away from you.
On top of that, when you injure the thing, it tries to run to an area more populated by its kind, and example being in Forest & Hills, in area 3, it'll run to area 10 where there's lots of bushes and Vprey to knock you down while you're trying to line up a swing.
Well, pressing the select button makes you kick. Myself...I never found a practical use for this except to wake up a stunned or sleeping person, maybe that IS the purpose. I certainly wouldn't go kicking bombs and such with it, nor would it be my attack of choice against...well...anything.
But with the great sword out and ready to swing, your kick is MUCH faster. Meaning, say you knock a drome down, roll closer to it, and you have your weapon out and you want to swing but you can see that the drome will jump clear of the blade when you swing, press select, the speed of your little kick sends it reeling for that precious second and allows you to hit it and hit it hard. I managed to kill dromes without them even getting a jump in edgewise...I just ran in, hit a few times, kicked, hit more time, and every time I needed an extra attack, I kicked it.
If you already knew this, or this is old news, sorry...I'm a little slow on the up-take here. I just figured it out. Lol!