Complex sentence: Even in his old age, he can easily best "Night" Rikuo and Muchi, normal demons feel so much "Fear" that he is invisible to them until he strikes, that's his "Meikyou Shisui".
Split into simpler sentences: Even in his old age, he can easily best "Night" Rikuo and Muchi. Normal demons feel so much "Fear" that he is invisible to them until he strikes, that's his "Meikyou Shisui".