JP authors sure love this "teleport into the path of a sword stroke mid-swing" trope for teh dramalamas, never mind now that nothing about the kinetics therein computes.
Aside from the obvious practical difficulties of actually getting there in time (a stroke worth the name takes a second tops to complete), there's the fact that sword cuts in general and curved sabres like the katana - which is designed to slash specifically with the *tip* (straight and flared machete-type blades have their "sweet spot", the optimal point of percussion, a bit below it) - in particular are really sensitive to proper distancing for effectiveness or lack thereof; interpose yourself into the trajectory like that and there's a very real chance what you'll get is whacked with the hilt instead because you're too close, or at worst suffer a relatively weak cut because you get hit by a portion of the blade close to the grip point where there isn't proper leverage and the stroke couldn't complete its intended arc for maximum velocity and energy...
Realistically the worst what the victim would usually suffer in these cases is a long but shallow superficial slash over the bones (reminder that the spine in particular is hella tough and the ribs are no joke either); definitely bloody and painful, but not terribly life-threatening - and certainly not the dramatic more-or-less instant and certain death that invariably gets depicted.
Would be a very different story with thrusts, which are quite insensitive to distances beyond the obvious practical necessities of getting the tip into the target in the first place, and typically at least disabling if not promptly deadly on the torso, but that's what happens when artists don't know squat about practical swordsmanship and are just running on the broken record of visually impactful clichés.