Nice
*I take a ''On guard'' position and I kick forward with my rigth foot with my arm extended (rigth one with the Bokken) lunging ahead while my left leg straights out and my left arm goes back from me to mantain my balance*
I'm starting to like this very much and I'm not talking about NB training

, now I'm gonna pay you more. U_U
xd I don't think I'm allowed to take any payment since I'm a Sempai, even though this isn't something that's "training", like the elements.
Very good.
Now, I want to make a point - what she does is absolutely perfect...for a one-handed lunge.
Although you won't need to put your left arm back in the same position she had it (fencing like she does is a sport, and therefor has some minor differences than a real sword fight - she mentions that it helps notate an actual lunge), your arm
will, more than likely, end up flared behind you in the same manner, and for the reason of balance, as well as it just being how your body moves. In short - when you do a one-handed lunge, no matter its position, you will, more than likely, find your left arm flared behind you unless you make a conscious effort to do otherwise.
(I want to demonstrate something - in real life, preform the lunge as she demonstrates, and then try it again, but make an effort to keep your left arm by your waist - you'll see how it actually affects your movement.)
Now, a great thing about the lunge is it's speed - because of the position you are in, even if the lunge is deflected, you can quickly move back into your standing stance, though you'll have to be careful to bring your sword back too.
Next is the two-handed lunge. This is preformed similarly to the lunge, except that you place both of your hands on the hilt of your sword.
While the one-handed lunge is more of a moving stab, the two-handed lunge is more of a thrust - you'll make the movements of the lunge, but thrust your sword at the opponent, it's power increased by the pushing force of two arms instead of one.
Please demonstrate the two-handed lunge, unless you need me too, in which case, please say so.
(I'd also like you to try doing this one in real life too, to get a feel for it - do the lunging motion, but act as if your holding your sword with both hands.)