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 August 2010
Otomo Sensei Sensei All cards that would go to your discard pile are instead permanently discarded from play. Reaction: When a player searches for and gets a card from his or her deck or discard pile, discard from play a card from your hand to discard the player's card from play.
Recruiting Drive Strategy Limited: For the rest of the turn, you may bring Followers into play from your discard pile. Treat the Followers as being played from your hand.
Can I use my Otomo Sensei's ability to discard the Follower my opponent is bringing into play from his discard pile? I believe the answer lies in the definition of the word "Search" which unfortunately is missing from Recruiting Drive.
Search To inspect a deck, or all cards in another area, in order to select one or more cards from it.
Thank you.
Alex Jones (rules official), 26 August 2010
Otomo Sensei Sensei All cards that would go to your discard pile are instead permanently discarded from play. Reaction: When a player searches for and gets a card from his or her deck or discard pile, discard from play a card from your hand to discard the player's card from play.
Recruiting Drive Strategy Limited: For the rest of the turn, you may bring Followers into play from your discard pile. Treat the Followers as being played from your hand.
Can I use my Otomo Sensei's ability to discard the Follower my opponent is bringing into play from his discard pile? I believe the answer lies in the definition of the word "Search" which unfortunately is missing from Recruiting Drive.
Search To inspect a deck, or all cards in another area, in order to select one or more cards from it.
Thank you.
Otomo Sensei was printed before a formal definition was attached to "Search". The intent of the current definition is to distinguish between effects that allow you to examine the top few cards of a deck and effects that let you examine and select from anywhere in the deck or discard pile. Recruiting Drive is clearly an example of the latter, and Otomo Sensei's Reaction can trigger off each such search.
Brook Cunningham (rules official), 26 August 2010
Addendum:
Alex is correct, but I'd like to point out that there's nothing really wrong with Otomo Sensei's wording in this case, despite its age.
Maruku, you seem to think that the effect that triggers Otomo Sensei (in this case, Recruiting Drive's) must explicitly include the word "search", but that is not the case. This is one of the reasons why "search" has a listed definition at all; so that one can tell what circumstances would trigger a card like Otomo Sensei. And what Recruiting Drive is doing fits exactly the definition of "Search".