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, 9 January 2012
If I play "Again!" on my Kensai and later that battle attach a Weapon say via "Glory of the Shogun" or "Readied Steel" may I use the Battle abilities of that weapon a second time despite the fact that it was not attached at the time I played "Again!"?
Second If I use Daigotsu Kanpeki to preform "Again" can I use his reaction after the resolution of "Again" to take additional action, if so dose that occur before or after the additional action granted by "Again!"?
Relevant text
Again! Battle: Chose your performing Kensai: Straighten him and all his Weapons. Battle abilities on his Weapons may be used a second time this turn. You may take an additional Battle action.
Daigotsu Kanpeki Reaction: After the resolution of a Battle action from a Strategy, if Kanpeki performed it: Take an additional Battle action.
Alex Jones (rules official), 10 January 2012
If I play "Again!" on my Kensai and later that battle attach a Weapon say via "Glory of the Shogun" or "Readied Steel" may I use the Battle abilities of that weapon a second time despite the fact that it was not attached at the time I played "Again!"?
Second If I use Daigotsu Kanpeki to preform "Again" can I use his reaction after the resolution of "Again" to take additional action, if so dose that occur before or after the additional action granted by "Again!"?
Relevant text
Again! Battle: Chose your performing Kensai: Straighten him and all his Weapons. Battle abilities on his Weapons may be used a second time this turn. You may take an additional Battle action.
Daigotsu Kanpeki Reaction: After the resolution of a Battle action from a Strategy, if Kanpeki performed it: Take an additional Battle action.
Attaching a weapon to a Personality who has been targeted by Again!, does not allow you to use its Battle abilties a second time this turn. The clause "his Weapons" is evaluated at the point in time when the effect is applied, which is immediately, in the case of an ongoing effect such as Again!'s. Compare Frenzy, which destroys the Personality's Followers through a delayed effect: "his attached Followers" is evaluated when the effect is applied - "Before the turn ends" - so Followers which have been transferred out of his unit are not destroyed by Frenzy.
For more information on "activating" vs "applying" effects, see Abilities and Actions, Action Resolution.
For your second question, see Additional action: When an additional action is granted while a non-Reaction action is in progress, the timing of the additional action is delayed: the opportunity to take it happens once the current non-Reaction action has ended, and once the opportunity to play Reactions to the end of the action has passed. This makes sure that Battle actions can not occur within other Battle actions, or Limited/Opens within other Limited/Opens. The additional actions granted by Again! (first emphasis) and by Kanpeki's ability (second emphasis) are both delayed to the same point in time, so the active player decides which action is taken first.