The Japanese term for a noodle refill in many tonkotsu ramen restaurants is kae-dama, also written kaedama.
With kae-dama, diners finish most of the noodles while leaving broth in the bowl, then order another serving of freshly cooked noodles. The refill usually does not include a new bowl of soup. This system is particularly associated with Hakata-style tonkotsu ramen in Fukuoka, where thin noodles cook quickly and can become soft if left in hot broth too long.
The custom also lets customers choose a different noodle firmness for the second serving, such as firm or very firm. Kae-dama is common in tonkotsu shops but is not universal across every ramen style or restaurant. It is therefore different from ordering a larger initial portion or replacing the entire bowl.