Last fall, Ai Nakajima, 40, tied the knot in Germany with her long-time partner, Kristina Baumann, a 32-year-old from Berlin. But in Japan, where they live, Nakajima and Baumann share the fate of all same-sex couples in committed relationships — the denial of the right to formally marry their partners.

The two will be among 13 LGBT couples to file lawsuits nationwide against the government on Valentine's Day on Thursday demanding that same-sex marriages be made legal — the first legal action of its kind in Japan.

They are claiming the denial of marriage rights is unconstitutional.