Noodle Shop Affair(2002)

Himitsu na Kankei

Ukyou, the spoiled only son of the most powerful mob boss in the region, is smitten at first sight with Kakeru, the cute son of a local ramen shop. But when he goes to declare his undying love, he discovers that thanks to the bullying of a rival mob, the ramen shop is deep in debt, Kakeru's father is in the hospital, and Kakeru is struggling to keep the place going on his own. Naturally, Kakeru now HATES yakuza. Fortunately, the kid is too dim to recognize Ukyou without his sunglasses and loud suits, so Kumichou-san (Mr. Mob Boss) whips off the sunglasses and becomes Ukyou-kun, a homeless guy who needs a job at the ramen shop to survive. Hijinks ensue.

(Source: Houbunsha, translated)

Note: Each volume has a different title.
Volume 1 - Himitsu na Kankei (秘密な関係)
Volume 2 - Naisho na Kankei (ナイショな関係)
Volume 3 - Honto no Kankei (ホントの関係)