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, 18 February 2010
IF my opponent has only 5 personalities (or only 5 legal targets for United) in play, and i Direct Approach one of them, can he not play United, since all of them are performing the action and one of them cannot perform actions?
United: Battle/Open: Target five of your non-Shadowlands Personalities, no two of whom share a Clan alignment: Give each of them +4F. Negate their movement home from other players' actions until the turn ends.
The Direct Approach: Open: Give a target Personality -1F for each of his keywords other than Clan alignments. If his Force is now 0, he may not perform actions.
Dan Jacobson (rules official), 18 February 2010
IF my opponent has only 5 personalities (or only 5 legal targets for United) in play, and i Direct Approach one of them, can he not play United, since all of them are performing the action and one of them cannot perform actions?
United: Battle/Open: Target five of your non-Shadowlands Personalities, no two of whom share a Clan alignment: Give each of them +4F. Negate their movement home from other players' actions until the turn ends.
The Direct Approach: Open: Give a target Personality -1F for each of his keywords other than Clan alignments. If his Force is now 0, he may not perform actions.
Assuming that The Direct Approach reduces that personality's force to 0, you are correct, that personality may not be one of the 5 personalities that perform United.