Obtaining a highest fame rating requires that you simply use a character that is of that nature, or by completing skirmishes that reward that type of fame. There is also an option to take jobs from your lord if you're an officer which reward additional fame of different variations. Each of these fames can go as high as fame 9, so you'll have to take part in many battles before unlocking each respective trophy.
It is advised you only do one of these fame choices per playthrough, as there are trophies also tied for seeing endings which are determined by your highest fame.
Brave characters are often those who are well known for their fierce abilities in battle such as Guan Yu or Lu Bu. While many of these styles are enjoyable, if you don't find one you enjoy you can simply create a character with this fame type and play through a scenario that way, earning brave fame with each battle.