The Japanese side announced the signing of its fourth former Barca player as the clubs, which faced each other in a pre-season match on Saturday, moved to formalise their growing links.
LaLiga champion Barca and Vissel Kobe announced the agreement of a knowledge-sharing partnership spanning marketing, commercial and staff management practices.
Scouting reports will also be shared and young players will have the opportunity to move between the clubs for training experience.
Vissel Kobe is owned by e-commerce company Rakuten, Barca's shirt sponsor and "main global partner" since 2017.
Iniesta left Camp Nou for the J.League in 2018 and has since been joined by former team-mates Villa and Sergi Samper.
Belgium international Vermaelen is the latest beneficiary of the link after Barcelona's decision not to renew his deal for a sixth season.
"When I came here, I had a very warm welcome and a lot of support," former Arsenal player Vermaelen said upon signing for his new club.
"I can't wait to start. I'm excited about it. I would like to do my best to improve the team."
Barca's clash with Vissel Kobe was its second pre-season outing, Ernesto Valverde's men having lost 2-1 to Chelsea earlier this week.