Anzu appears loud and confident, but she suffers from artist’s block after her best friend and rival, Koudai, publicly humiliated her. She sees the tunnel as material for a masterpiece.

The tunnel waits. But so does summer. The film’s final gift is that it lets you decide which one you’d rather walk toward.

The film follows two teenagers who form an unlikely partnership to explore the tunnel's secrets:

The title "Tunnel to Summer, Goodbye Exit Full" is intriguing, suggesting a narrative that could encompass elements of youth, transition, and perhaps the bittersweet nature of goodbyes. The imagery of a tunnel leading to summer evokes a sense of passage or journey, not just physically but potentially metaphorically. Summer, often a season associated with freedom, warmth, and endless possibilities, could symbolize a period of growth or a significant phase in the characters' lives.

The tunnel’s threshold—its exit—is labeled with "sayonara," the Japanese word for goodbye. This explicit naming turns departure into deliberate act. Saying goodbye is ritualized: a sequence of small gestures, an exchange of objects, words that tremble with unsaid meanings. The presence of a "goodbye exit" suggests agency—an opportunity to choose closure rather than be carried away by circumstance. Yet it also raises questions about who is allowed to pass through that exit, and what remains on the inside.