The host at this IP address is running a malware botnet controller which is being used to control infected computers (bots) around the globe using a trojan horse.
OskiStealer botnet controller located at 104.21.71.57 on port 80 (using HTTP POST):
hXXp://t-shinwa-jp.com/admin//6.jpg
$ dig +short t-shinwa-jp.com
104.21.71.57
Other malicious domain names hosted on this IP address:
www.elecdeer.com 104.21.71.57
t-shinwa-jp.com 104.21.71.57