Traveling to the world of Naruto, a panel awakened.
Your proficiency will increase with practice, and it will increase faster in actual combat. You can also learn it secretly by watching others use ninjutsu - isn't this just an ANBU custom-made plug-in?
So, while other ANBU newcomers were struggling in the shadow of their missions, the protagonist lived a happy life of refreshing panels at the ANBU training ground.
Kakashi: "Why are you so active in every mission?" Protagonist (looking at the +3% Raikiri progress on the panel): "I love work." Third generation: "Is this ANBU newcomer a little too diligent?" Danzo: "This person must be included in the root." Protagonist (panel pop-up: Your teleportation technique has exceeded Lv. 10, And your speed exceeds Golden Flash): "Sorry, what are you talking about? I'm leveling up."