You can put a systemd file to run at startup. Create a file as root in:
/etc/systemd/system/kbd_mode.service
Then fill it with:
[Unit]
Description=Set keyboard mode to unicode on boot
[Service]
Type=forking
ExecStart=/usr/bin/kbd_mode -u
[Install]
WantedBy=multi-user.target
Then you need a way to add it to systemctl. I cannot remember completely! Demm knows better. But I guess you should run:
systemctl enable kbd_mode.service
systemctl kbd_mode start