愚弟 ぐてい
gutei

Noun

1. (one's) younger brother

Humble
Noun

2. foolish younger brother

ども、愚弟 ぐていがお世話 せわになってるようで。
domo gutēga osewani natteru yōde.
Thanks, I hear you've been taking care of my little brat of a brother.