Kinsei Tokkyuu Gaiden

Natsukasa, the 52nd of the White Chain, infiltrates a French Foreign Legion fortress to investigate, and meets a company commander named Louis, who has a void in his eyes...? Satetsu and Eustace travel the world to retrieve the mysterious power left behind by Venus. The princesses continue to research languages while fighting against the Pure Lands, and the Yuezhi who protect them. And Sabimaru, who is raising a daughter with Venus. This is a collection of exquisite spin-off stories from the hugely popular series, depicting some untold stories from the century-old love story between Sabimaru and Venus, as well as the aftermath of their journey.

(Source: Shinshokan, translated)