Roaming Village Ninjas

Who They Are

Village ninjas out on the roads of the overworld: either a squad of a Jonin leader with three Genin following in file (fanned out behind), or a lone ANBU.
Genin are tier 1 (100 health). Jonin and roaming ANBU are tier 3 (380 health; the ANBU is "as strong as a Jonin"). Each Genin uses one of four looks (girls and boys).
Their village shows in their gear and name, such as "Leaf Genin", "Leaf Jonin" or "Leaf ANBU".

The leader (or lone ANBU) wanders a winding road of its own: legs of 10-23 blocks with gentle turns, a sharp turn now and then, and an occasional rest to look about. It avoids water and steep climbs (over 8 blocks).
Followers keep their place behind it and teleport to catch up if more than 30 blocks behind. If the leader dies, another member of the squad takes over.
Passive to players until hit. They fight only hostile NPCs (Akatsuki, rogues, outlaws), never peaceful ones, and peaceful NPCs leave them alone.
They despawn only when no player is within 112 blocks, and a squad always leaves together. They are not kept when the world is saved, so they never pile up out of sight.

Each has exactly one basic nature, picked when it first appears: most often its village's own nature (Leaf fire, Sand wind, Mist and Rain water, Stone earth, Cloud lightning), sometimes one of the other four.
Genin fight with that nature's basic jutsu (at least two, topped up from higher tiers if needed). Jonin and ANBU use its intermediate, advanced and expert jutsu.

Units appear near players in the overworld, now and then. There are at most 2 units (squads or lone ANBU) for each player online, and never more than 8 in the world.
Spot: 48-96 blocks from the player in a random direction, on solid, dry ground, with no player within 24 blocks of it.
Near the villages they are thickest: they turn up most often within 500 blocks of a village centre (the village's lands), less often within 1,200 blocks (the outskirts), and only now and then out in the wilds.
Crowding limit: no new unit if there are already 2 units within 160 blocks (in a village's lands) or 1 unit within 160 blocks (elsewhere). When there are more units than these limits allow, the ones that aren't fighting are sent away, the furthest from any player first.
Which village: in a village's lands or outskirts, most are that village's own ninjas, with the odd squad from elsewhere; out in the wilds, they can be from any village.
Squad or ANBU: most units are squads of four; a lone ANBU is the rarer sight.

When killed by a player (who hit it recently), each can drop the chakra fragment of its own nature. ANBU drop them most often, then Jonin, then Genin.
Killing one costs its village 5 respect. The killer's honor (if they have a village): -15 if it was their own village's ninja, -10 if an allied village's, +5 otherwise.