The "I am proud" etc. thing is actually a quote from Hamlet. He's self-aware of how he truly is, and since the quote was relevant to him, he used it. But, basically, Mahiro is one of the characters in the series who references Shakespeare often, especially if it applies to him or the situation he's in. I hope this answers your concern!
Mahiro apper here!
The "I am proud" etc. thing is actually a quote from Hamlet. He's self-aware of how he truly is, and since the quote was relevant to him, he used it. But, basically, Mahiro is one of the characters in the series who references Shakespeare often, especially if it applies to him or the situation he's in. I hope this answers your concern!