Negima!? Magister Negi Magi - Season 1 Episode 9 You hide the 'heart' with a 'sword' and read it as ninja. It is a little different than how you write 'serious' and read it as 'for real'.
Out in the woods for Magic Training Camp, Negi attempts to teach his partners the basics of wizardry, but haunting dreams of his father leave him fatigued and vulnerable.