Good Reference: a twitter in Japanese)

1. Jailbreak your iPhone.
2. Open cydia and add a source: repo.hackyouriphone.org.
3. install CommCenter Patch.
4. Make a .ipcc from KDDI_UQ_LTE_only_jp.bundle. See make .ipcc.
Docomo_jp.bundle did not work for me.
5. Inject it to your iPhone via iTune.
6. Turn on Airplane mode and then off. check whether Rakuten Antenna appears or not.
7. If airplane mode on and off does not work, reboot it (and jailbreak if your phone is semi-tethered or semi-untethered.)
Reboot and re-jailbreak were necessary for iPhone7 in my case. Airplane mode was not enough.