To open the New Gaudi Bar in Yakuza 6, you first need to complete a few Sub Quests. The New Gaudi Snack Bar is located in Onomichi and is locked on your first visit there.
Starting at chapter 4 you will be able to trigger a random talking event in Onomichi where you will be invited to the baseball field. The sub quest “Assemble the Team” requires you to take a taxi to the baseball field. Play a game and return to Onomichi.
Your new goal is to collect baseball players. One of these players is the key to opening the New Gaudi Bar and he is located near the bar. Find this sub quest called “We Need a Ringer” and convince Moritsuka to join the team.
After the conversation you complete the sub quest and unlock the Gaudi Bar.