If the girls aren’t changing the way they speak when they’re undercover then he really needs to have his eyes checked![]()
It's actually done reasonably well in the LNs. The more time they spend around each other, the more obvious it becomes who they really are. First-arc girl stays fooled for about five seconds once he helps take on her situation. Second-arc girl recognizes him, too, but is in some heavy denial about it (even her subconscious is like "take a hint girlie").