1. A method performed under control of a game server, the method comprising: calculating a degree of closeness between a first character and a second character positioned in a same space of a virtual game, wherein the calculating the degree of closeness is based at least in part on one of: a frequency of occurrences in which the first character and the second character are included in a same character party or a frequency of occurrences in which the first character and the second character execute a collaborative attack against an opposing character, wherein each of the frequency of occurrences in which the first character and the second character are included in the same character party and the frequency of occurrences in which the first character and the second character execute the collaborative attack against the opposing character is assigned a different weight coefficient, wherein the calculating the degree of closeness is based on the assigned weight coefficient, and wherein the closeness corresponds to a relationship or communication between the first character and second character; calculating a level of detail (LOD) for the first character, wherein the calculation of the LOD is based at least in part on the calculated degree of closeness; controlling a display definition of the first character, wherein the controlling the display definition is based at least in part on the calculated LOD, and wherein the controlling the display definition includes controlling a number of polygons used to render the first character; and rendering the first character with the controlled number of polygons, to enable the first character to be displayed with different display definition, based on attention of a user, with respect to other characters positioned in the same space of the virtual game.