Uchi No Otouto Maji De Dekain. -

The nuance is not just "he is large," but "I’m telling you, my little brother is unreasonably large." It implies disbelief, mild distress, and often—depending on context—a tinge of romantic confusion.

Despite the exaggerated "size" element, the bickering, secret-keeping, and underlying affection between the siblings feel grounded in reality for many readers. uchi no otouto maji de dekain.