As the title suggests, despite being the fifth game in the series it takes place before all the other titles timeline-wise (two years before the first game, Samurai Spirits)
Many of the new characters such as Gaoh and Yoshitora were designed by Kenshin creator Nobuhiro Watsuki who has said in the past of being a big fan of the Samurai Spirits series.
Trigun creator Yasuhiro Nightow is also mentioned in the credits and is said to have designed a few of the characters. However, it is currently unknown who exactly he designed.