Genma Note locations幻魔雑記
Every Genma Note sits alone in its own chest, and all 23 chests are hidden until you use Oni Vision. Most appear only after a particular mission, usually the one where you first fight that enemy or a later one, so each row gives the condition. 6 are there from the moment you reach the area.
Collecting all 23 unlocks the Genma-ologist achievement. The Yoshitsune note is the last one; its chest appears at Rokudo-chinnoji Temple after you finish the game.

Genma Note: Rasho-gan
Higashioji Street district, Eastern Kyoto
Appears after clearing The Curse of Kiyomizu-zaka Slope. Hidden: shows up with Oni Vision.

Genma Note: Benkei
Gojo-ohashi Bridge, Eastern Kyoto
Appears after clearing Bloodbath on the Bridge. Hidden: shows up with Oni Vision.

Genma Note: Ifuu
Northeast of Kamo River - East, Eastern Kyoto
Appears after clearing Storm Chaser, A Tempest at the Temple. Hidden: shows up with Oni Vision.

Genma Note: Burai
Northeast of Kamo River - East, Eastern Kyoto
Appears after clearing Storm Chaser, A Tempest at the Temple. Hidden: shows up with Oni Vision.

Genma Note: Yoshitsune
Rokudo-chinnoji Temple district, Eastern Kyoto
Appears after finishing the game. Hidden: shows up with Oni Vision.

Genma Note: Byakue
Kiyomizu-zaka Slope district, Eastern Kyoto
Appears after clearing The Curse of Kiyomizu-zaka Slope. Hidden: shows up with Oni Vision.

Genma Note: Dohatsu-ten
East of Gojo Street - East, Eastern Kyoto
Appears after clearing The Roots of All Evil. Hidden: shows up with Oni Vision.

Genma Note: Hitotsume Gasa
Northeast of Kamo River - East, Eastern Kyoto
Appears after clearing The Stage is Set at Kiyomizu. Hidden: shows up with Oni Vision.

Genma Note: Togemaru
Higashioji Street district, Eastern Kyoto
There from the start. Hidden: shows up with Oni Vision.

Genma Note: Kubi Akari
Kamo River - East district, Eastern Kyoto
Appears after clearing Kyoto, Corrupted. Hidden: shows up with Oni Vision.

Genma Note: Kogai
North of Gojo Street - West, Eastern Kyoto
Appears after clearing Patching up the Pouch. Hidden: shows up with Oni Vision.

Genma Note: Sasaki Ganryu
Nio-mon Gate district, Kiyomizu-dera Temple
Appears after clearing The Stage is Set at Kiyomizu. Hidden: shows up with Oni Vision.

Genma Note: Hitotsume Sho
Nio-mon Gate district, Kiyomizu-dera Temple
Appears after clearing The Stage is Set at Kiyomizu. Hidden: shows up with Oni Vision.

Genma Note: Daidara
Kiyomizu-dera Temple: south of Shrine Grounds
Appears after clearing The Stage is Set at Kiyomizu. Hidden: shows up with Oni Vision.

Genma Note: Chijiko
Underground Laboratory: near Underground Level 3
There from the start. Hidden: shows up with Oni Vision.

Genma Note: Kogashira
Underground Level 3 district, Underground Laboratory: Underground Level 3
There from the start. Hidden: shows up with Oni Vision.

Genma Note: Greater Nue
Palace Entrance district, Kyoto Imperial Palace
Appears after clearing What Lurks in the Shadows. Hidden: shows up with Oni Vision.

Genma Note: Nue
Nijo-jo Castle Entrance district, Nijo-jo Castle
Appears after clearing What Lurks in the Shadows. Hidden: shows up with Oni Vision.

Genma Note: Oboro Garasu
Cave Area district, Mount Oe: Valley
There from the start. Hidden: shows up with Oni Vision.

Genma Note: Hirehime
Cave Area district, Mount Oe: Valley
There from the start. Hidden: shows up with Oni Vision.

Genma Note: Shuten Doji
Castle Entrance district, Mount Oe: Castle Courtyard
Appears after clearing The Demon on the Mount. Hidden: shows up with Oni Vision.

Genma Note: Mohja
Nine-story Pagoda district, Arashiyama: Temple
There from the start. Hidden: shows up with Oni Vision.

Genma Note: Dokyo
Horin-ji Temple district, Arashiyama: Hozukyo Gorge
Appears after clearing In the Light of an Icy Moon. Hidden: shows up with Oni Vision.