The Ninja Tabi are footwear that increases a unit's movement by 2 (compared to the dash boots +1). You get them by beating the "Shadow Clan" mission, which appears late in the game.
It's a shame you can only get one Ninja Tabi... if Steal: Accessory allowed you steal shoes, you could have as many of them as you want. Oh well. There's always the Sequence and Peytral for sluggish Paladins.