21 cards where the color identity ≤ U and the card types include “ninja”

A-Futurist Operative (Kamigawa: Neon Dynasty #A-53)
A-Moon-Circuit Hacker (Kamigawa: Neon Dynasty #A-67)
A-Prosperous Thief (Kamigawa: Neon Dynasty #A-73)
A-Thousand-Faced Shadow (Kamigawa: Neon Dynasty #A-86)
Covert Technician (Kamigawa: Neon Dynasty #49)
Futurist Operative (Kamigawa: Neon Dynasty #53)
Higure, the Still Wind (Planechase Anthology #18)
Invasion of Kamigawa // Rooftop Saboteurs (March of the Machine #62)
Invasion of Kamigawa // Rooftop Saboteurs (March of the Machine #62)
Mistblade Shinobi (Planechase Anthology #20)
Mist-Syndicate Naga (Modern Horizons #58)
Moonblade Shinobi (Modern Horizons #59)
Moon-Circuit Hacker (Kamigawa: Neon Dynasty #67)
Moonsnare Specialist (Kamigawa: Neon Dynasty #70)
Ninja of the Deep Hours (Commander 2018 #95)
Phantom Ninja (Modern Horizons #62)
Prosperous Thief (Kamigawa: Neon Dynasty #73)
Saiba Cryptomancer (March of the Machine #76)
Saiba Syphoner (Alchemy: Kamigawa #11)
Sakashima's Student (Planechase Anthology #24)
Thousand-Faced Shadow (Kamigawa: Neon Dynasty #86)
Walker of Secret Ways (Planechase Anthology #27)

The arc of my blade has carved a path of light to the end of these results.