Here is the full list of all 20 Ikai achievements.
Complete every seal without losing or repeating it
Get all the collectibles
Get all the yokai pages
Get the katana in less than 1 minute
Draw the correct pattern without any mistake
Get the right instrument in a single attempt
Go unnoticed escaping from the forest
Toss the coin from a far distance
Don’t get burned on the way to the shrine
Complete the ultimate ritual
Wield the murder weapon
Break every destructible object with the katana
Complete the third purification ritual
Complete the second purification ritual
Escape from the forest
Complete the first purification ritual
Reach the unholy shrine
Wake up after the opening of the gate
Tag your sister in less than 1 minute
Write three seals for the villagers