Drinking Soup to the Last Drop (完食・完飲 - Kan-in)
The act of lifting the heavy ramen bowl with both hands and drinking the soup down to the very last drop ('Kan-in'). While not mandatory, it is the ultimate non-verbal sign of appreciation to the ramen chef.
Ramen chefs spend up to 20+ hours simmering bones, kelp, and seafood to extract the perfect umami. Seeing an empty bowl return is their greatest pride. Some bowls even feature hidden messages like 'Thank you' printed on the inside bottom.
It is completely fine to leave broth for health reasons. However, if the bowl was absolutely life-changing, lift it up, drink it clean, and proudly show the empty bottom to the kitchen as you say your thanks.
What is the correct understanding of drinking the soup to the last drop ('Kan-in')?