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.
Tasu Sensei has a reaction (I'm assuming an interrupt now) that reads: Reaction: Before another player loses Honor, negate the loss. Gain Honor equal to the amount negated.
If I cause a player using the stronghold Citadel of Daigotsu (You will not gain or lose honor) an honor loss, can I use Tasu Sensei to gain honor or not?
What about Obsidian Halls of the Lost (You DO not gain or lose honor)?
Both "do not" and "will not" are negation clauses and will apply always prior to other modifications on the gain, so the honor gain does not exist when you try to modify it with Tasu Sensei, regardless of the non-Reaction timing.
And do not assume that all Reactions will be instantly turned into Interrupts, because odds are that most of them will remain as Reactions, with Legacy and BigDeck rules allowing for keeping the old designator still working in those formats.