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, 20 February 2012
What would happen in this situation? Player A assigns with Shosuro Toson Xp2 and 2 Naval personalities, Player b Defends with one Paragon person. After engaging player A declares Naval Invasion with one of the naval personalities, Player B then uses Grateful Reward and attaches a follower, Player A then uses Shosuro Toson Xp2's reaction. Who must perfom the first action?
Relevant Text
Naval Invasion: Reaction: After engaging, once per battle, if you are the Attacker and your current army has more Naval cards than the side oppos¬ing it, choose your performing Naval Personality: You have the first opportunity to take a Battle action, which he must perform.
Shosuro Toson Xp2 Reaction: After engaging at Toson's battlefield: Discard a card from the current battlefield's province.If this discarded a Personality, you have the first oppurtunity to take a Battle action in this battle, which must be performed by Toson
Grateful Reward: Reaction: After engaging, choose your performing Samurai at the current battlefield: Create a 1F Ashigaru • Cavalry Follower and attach it to him. If he is a Paragon, gain 2 Honor and draw a card.
Jon Palmer (rules official), 20 February 2012
What would happen in this situation? Player A assigns with Shosuro Toson Xp2 and 2 Naval personalities, Player b Defends with one Paragon person. After engaging player A declares Naval Invasion with one of the naval personalities, Player B then uses Grateful Reward and attaches a follower, Player A then uses Shosuro Toson Xp2's reaction. Who must perfom the first action?
Relevant Text
Naval Invasion: Reaction: After engaging, once per battle, if you are the Attacker and your current army has more Naval cards than the side oppos¬ing it, choose your performing Naval Personality: You have the first opportunity to take a Battle action, which he must perform.
Shosuro Toson Xp2 Reaction: After engaging at Toson's battlefield: Discard a card from the current battlefield's province.If this discarded a Personality, you have the first oppurtunity to take a Battle action in this battle, which must be performed by Toson
Grateful Reward: Reaction: After engaging, choose your performing Samurai at the current battlefield: Create a 1F Ashigaru • Cavalry Follower and attach it to him. If he is a Paragon, gain 2 Honor and draw a card.
The Naval Personality. Similar to your other question, in this case Toson is attempting to stack the ability to go first with the already existing ability granted by Naval, and therefore the effect (and its differing restrictions) fails.
However, since Toson is insistent on being a pain in the butt, please reference here for a situation with a slightly different outcome.