I think I've seen a ruling earlier on this forum, by Zen. I can't find it, it's too deep, and this crippled-search function and all. So sorry no link.
This ruling stated that Bokkai :
Mantis Clan Pirate
Battle: Bow Bokkai: If Bokkai is in the current battle, Ranged 5 Attack. This actions target may be at any battlefield or the Defenders home.
cannot target himself because he does not remove the need to target another player's card.
Let's quote the rulebook now :
Making Ranged Attacks
Some cards have the ability to make ranged attacks. A ranged attack must target a single card opposing the card or cards making the ranged attack: either a Follower or a Personality with no Followers. Ranged attacks cannot target Provinces or types of cards other than Followers and Personalities. A ranged attack destroys its target card if its strength (which may be 0) is greater than or equal to its targets Force. Excess strength yields no extra benefit. If the strength is less than the targets Force, nothing happens.
Nothing there is written about the card needing to be another player's. There is only the "opposing" thingy. And it is waved per Bokkai's text.
Moreover, to thing of it, you can oppose your own units (writ of conscritption / Ninube Ogoku). In that case would your ranged attack should be able to target one of the card you control opposing another card you control (with a ranged attack) ? I believe so.
At least I have no reason to think anything else (except your ruling, which doesn't appear in the archive clearly either). I'm willing to believe you... If you explain me what made you think things were so.
Thanks for your time.
(And citing cards such as Arrows From the Wood or Tsuruchi Tech is probably irrelevant, because is has been ruled that "opposing" on such a card means "opposing a card you control")
Togashi Imura