Like a Dragon Gaiden: The Man Who Erased His Name

In order to be fully bounded with a member, you need to achieve fighter level 20 and bond level 3.

Bond Level increases by participating in team matches or by purchasing champagne at the Fighter's Lounge bar (located near the pool).

Fighter Level increases through team fights or by using them instead of Joryu in single matches. You can also engage in training sessions with the individual marked with the gym icon in the lounge, although it requires time. However, I don't recommend this method due to its low experience gain compared to the time required; farming battles is much faster.

Within the lounge, you can also purchase presents to gift to fellow fighters. The higher your rank, the better items you can acquire.

To completely bond with a clan member you must get their bond level to max which is level 3, as well as get their fighter level maxed which is level 20.

You gain experience for both by either fighting along side them in team battles, or by purchasing the items that raise bond and fighter exp from the shop in the fighters lounge area in the Castel.