1. A method of generating a character image in which multiple characters, including a player character, a three-dimensional character drawn by three-dimensional polygon data and a two-dimensional character drawn by two-dimensional sprite data, are drawn in a virtual three-dimensional space, the character image displaying a conversation field in which the player character is enabled to have a conversation with another character, the method comprising: determining that a character satisfying a predefined non-display condition is not drawn in the virtual three-dimensional space among characters positioned in a field of view of a virtual camera; drawing, by a graphics processor, a character that satisfies a predetermined two-dimensional display condition as the two-dimensional character among the characters positioned in the field of view of the virtual camera; drawing, by the graphics processor, a character that does not satisfy the two-dimensional display condition as the three-dimensional character among the characters positioned in the field of view of the virtual camera; displaying, by the graphics processor, a conversation allowable mark in a vicinity of a character that is enabled to have a conversation with the player character among the characters drawn in the character image, the conversation allowable mark indicating that the character that is enabled to have a conversation with the player character is enabled to have a conversation with the player character; receiving a selection of one character among the characters in the vicinity of the conversation allowable mark; executing a movement control process in which the player character moves to a vicinity of the selected one character; and executing a reply control process in which the selected one character replies to a conversation request from the player character by considering that the conversation request is received when a movement is terminated, wherein the two-dimensional character drawn in the character image is enabled to have a conversation with the player character, wherein a conversation is executable with any conversation allowable character in the virtual three-dimensional space even when the conversation allowable character is located distantly from the player character, and wherein the predefined non-display condition is defined such that a character having a small external size achieves a non-display state when a distance between the character having the small external size and the player character is relatively small, and such that a character having a large external size does not achieve the non-display state until a distance between the character having the large external size and the player character is relatively large.