Eiji's interaction with Suga in "Banana Fish" plays a crucial role in shaping his actions toward the end of the story. Suga, who is a journalist and a mentor figure to Eiji, represents a connection to the outside world and a source of guidance. Their relationship highlights themes of trust, loyalty, and the impact of mentorship.

As the story progresses, Eiji's experiences with Suga help him to understand the complexities of the world around him, particularly the dangers associated with the criminal underworld that he has become entangled in due to his relationship with Ash. Suga's advice and support encourage Eiji to think critically about his choices and the consequences they may have, not just for himself but also for Ash.

Toward the end of the series, Eiji's interactions with Suga reinforce his determination to protect Ash and to take action against the forces that threaten them. Suga's influence helps Eiji to realize the importance of standing up for what he believes in, even in the face of overwhelming odds. This culminates in Eiji's decision to confront the challenges ahead, demonstrating growth and a deeper understanding of his own values and the stakes involved in his relationship with Ash.

In summary, Suga's mentorship and the bond they share significantly impact Eiji's character development, ultimately guiding him to make pivotal decisions that reflect his commitment to Ash and his own moral compass.