Comprising of nine states, EU9 has grown to be a significant component of the EU. The EU9 became part of the EU in its 3rd growth phase in 2004, implanting diversity and fresh perspectives into the EU society.

The EU9 countries here include Malta, Estonia, Slovenia, Slovakia, Czech Republic, Hungary, Latvia, Lithuania, and Poland. These countries each have made meaningful efforts towards furthering the goals of the European Union.

Therefore, comprehending the responsibility EU9 plays in the European Union is required for any study relating to European economics, politics, or international relations.

Right from their admission, the states belonging to EU9 have given significantly towards shaping the European Union's policies. Their geographical location gives critical strategic advantages, turning them a crucial part of the defense and security strategies of the EU.

Additionally, these states have significantly contributed to the European Union's financial strength. The EU9 nations' rapid economic growth and keen integration into the EU market has resulted in increased trade with other EU members.

The social contribution of the EU9 is equally significant. These nations bring deep historical backgrounds, unique cultural practices, and diverse languages, thus enhancing the variety of the EU.

The addition of EU9 has also impacted the political dynamics within the EU. With their presence, the power dynamics have altered, with new coalitions and alliances forming.

In conclusion, the roles played by the EU9 countries are substantial. From economic influence to cultural richness, and from security strategies to political dynamics, EU9 has fortified the European Union's core strength. As such, an in-depth understanding of the EU9 is vital to fully grasping the intricacies of the European Union.