If you want your client connected to a Japan VPS, but you want a US IP.

Client <--> Japan VPS <--> US VPS

1. Setup Shadowsocks server as usual on US VPS.

2. On Japan VPS, enable forwarding. Replace US_VPS_IP and JAPAN_VPS_IP with actual IP:

    sudo su
    echo 1 > /proc/sys/net/ipv4/ip_forward
    iptables -t nat -A PREROUTING -p tcp --dport 8388 -j DNAT --to-destination US_VPS_IP:8388
    iptables -t nat -A POSTROUTING -p tcp -d US_VPS_IP --dport 8388 -j SNAT --to-source JAPAN_VPS_IP
   

3. Set your server to JAPAN_VPS_IP:8388 on your client.

For those who want more control and better performance, use haproxy instead. You can also enable load balance by adding multiple servers.

For Debian 7.0:

On Japan VPS. Append the following line to /etc/apt/sources.list

deb http://ftp.us.debian.org/debian/ wheezy-backports main

Run

apt-get install haproxy

Edit /etc/haproxy/haproxy.cfg

global
        ulimit-n  51200

defaults
        log	global
        mode	tcp
        option	dontlognull
        contimeout 1000
        clitimeout 150000
        srvtimeout 150000

frontend ss-in
        bind *:8388
        default_backend ss-out

backend ss-out
        server server1 US_VPS_IP:8388 maxconn 20480

Then run haproxy -f /etc/haproxy/haproxy.cfg