This is a spar, after all. Tonbokiri did tell him to come at him, and Minato has to respect that order if he wants to learn, right? Tonbokiri definitely knows better than him when it comes to sparring like this, so--

Minato does avoid the slow attack easily, moving out of the way on automatic, and finally, finally he whips himself into shape enough to actually make a go at Tonbokiri properly; his sword is shorter than the spear by far, so as soon as he's within Tonbokiri's reach, he goes for it, twisting to bring his sword around towards Tonbokiri's side, lacking in technique but nonetheless steady.

Still, even though he's sure that Tonbokiri will be able to handle it just fine, there's still part of him that's nervous, attacking another actual person with naked steel, and that hesitance is plain in his strike.