Which word describes a manner that is openly straightforward and lacking in worldliness?

The term that best describes a manner that is openly straightforward and lacking in worldliness is "ingenuous." This word conveys a sense of honesty and a lack of pretense, suggesting that a person is sincere and straightforward, often characterized by an absence of guile or deceit. "Ingenuous" implies a naturalness and authenticity that reflects a straightforward demeanor, often associated with someone who has not been influenced by the complexities of the world around them.

In contrast, while "naive" also suggests a lack of sophistication and experience, it carries a connotation of being overly simplistic or unrealistic about the world. "Innocent" indicates purity and a lack of malice or wrongdoing but does not necessarily encompass the straightforwardness aspect. "Simple" might imply straightforwardness but lacks the nuanced sense of sincerity and absence of guile that "ingenuous" encapsulates. Thus, "ingenuous" is the most fitting choice for the description provided.