Otaidokan has a pending expansion with more options  and a GM Agenda. I will possibly give a good wash to The Forge of Tokurenkai and expand it with images to keep all things together. 

I first thougt of using Dungeon World's DM Agenda as a base, then went for Urban Shadows' as the tone is more for intrigues and politics. I might still use Urban Shadows as a base but I have found as well Thousand Arrows, another Samurai-themed Pbta ttrpg which, with some adjustments, could work well.

Here is my first draw:

GM AGENDA

• Fill the Sapphire Island with war and intrigues.
• Make the players’ character choices matter 
• Play with a mind unfettered 
• Always say what your rules, honesty, consistency, and principles demand

PRINCIPLES OF THE GM

• Paint the war in blood and ink 
• Address characters, not players 
• Cloak moves in the fog of war 
• Draw maps, leave blanks 
• Give everyone names, pasts, and objectives.
• Treat everyone according to their status 
• Ask questions and build on the answers 
• Be a fan of the players’ characters 
• Sometimes, let someone else decide

GM MOVES

• Separate them. 
• Spring a trap. 
• Harm them. 
• Dishonour them.
• Drain their resources. 
• Threat something precious. 
• Show them their gear’s limitations . 
• Turn nature against them. 
• Shift range (fists, spears, arrows …) and/or scale (strategic, tactical, personal …). 
• Tempt an individual to betray the group. 
• Question their loyalty 
• Question their training. 
• Reveal their liege’s weakness. 
• Reveal their subject’s strength. 
• Put all the attention on them. 
• Announce an unwelcome truth