A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 26 July 2009
Situation:
Player A has Armor of the Heavens attached to his personality. Player B has a monk in play. The personalities are opposing on another in battle at a province. It is Player B is active and it is his turn.
Player B plays Hand of Osano-Wo targetting the Armor of the Heavens on Player A's personality.
Question: Can player A use the reaction of Armor of the Heavens?
I was not sure after consulting page 14 of the Celestial Rulebook - "... When a unit is targeted, this targets its Personality..."
Hand of Osano-Wo: Battle: Target your unbowed Monk, and bow him if he is not Tattooed: Destroy a target enemy attachment. If its Personality now has no Followers, you may make a Ranged 3 Attack targeting him.
Armor of the Heavens: Political Reaction: After another player targets this Personality with an action: Either gain 2 Honor, or have the other player lose 2 Honor.
Brook Cunningham (rules official), 26 July 2009
Player B plays Hand of Osano-Wo targetting the Armor of the Heavens on Player A's personality.
Question: Can player A use the reaction of Armor of the Heavens?
I was not sure after consulting page 14 of the Celestial Rulebook - "... When a unit is targeted, this targets its Personality..."
No, you cannot use the Reaction.
Note, the rule you quote says "When a unit is targeted" not "When a card in the unit is targeted".
Hand of Osano-Wo targets the attachment, then the Personality, never the unit as a whole. For an example of such an instance, see Dramatic Assassination.