"My younger brother is seriously huge [part] 25."
If you want, I can:
If you are looking for Chapter/Volume 25 of a similarly named series, it may be "Uchi no Otouto-domo ga Sumimasen" Our Younger Brothers are Sorry ). Unlike the adult title above, this is a mainstream family-love comedy uchi no utouto maji de dekain 25
By using "dekain," the speaker signals a lower register of speech—intimate, rushed, and unpolished. This adds to the drowsy, half-awake feel of the entire utterance. It is as if the speaker is so utouto themselves that they cannot finish their words properly. "My younger brother is seriously huge [part] 25