What is the fine-grained topic of the following text: He is joined by three buddies – Kawashima Ryunosuke (Tsukamoto Takashi), a gangster serving a 10-year sentence for a murder; Takimoto Kuya (Ueda Tatsuya), a former host sentenced to 4 years for violation of the stimulant drugs control act and obstructing officers from performing their duty; and Kagami Shun (Suda Masaki), an ex-dispatch rider sentenced to 3 years for violating the stimulant drugs control act as well. Only return the topic.
Criminal backgrounds of four characters in a story