Board Thread:General Discussion/@comment-121.7.195.67-20161128145037/@comment-28150993-20161207034837

It's not really about being brothers (point in case: Kanesada duo are not brothers but their costumes are similar because they're from the same school), it's just that Sanjou lacks costume-uniformity with each other compared to all other schools. Their design points are quite different from each other in both normal and internal affairs costume. For other schools, even if their normal costumes don't seem similar, their internal affairs are the same design--or vice versa. Or in Kotetsu's case, their inner costume  (and their habit of stripping during shinken hissatsu)  is the same.

The only ones having same style inner in Sanjou are Kogitsunemaru and Mikazuki (the ones directly stated as made by Sanjou Munechika and drawn by the same artist). And even then they don't refer to each other as brothers in any material so far. Much less the other 3 Sanjou blades.

In touken ranbu let's think of the family relationships based on in-game/canon information instead of real-life information because the game devs tend to change stuffs to fit, e.g. Taroutachi and Jiroutachi are created by different smiths, from different areas, in different eras, and originally have different names (Taroutachi was actually an Aoe blade and smithed later than Jiroutachi), but they consider each other siblings in-game (though you can also argue that Jiroutachi called him Aniki as a symbol of respect). Or about Higekiri and Hizamaru, with their swordsmiths being arguable (same? different smith?), but since both characters think of each other as siblings, I think that's the only important thing.

Even for Kotetsu and Horikawa's cases, even though Nagasone is a fake, and Horikawa might not be a real Horikawa blade (made by Horikawa Kunihiro the swordsmith), if the characters themselves call each other siblings, then that's what's important in my opinion.

BUT! I said all of this (and my previous comment) because Sanjou don't have any interactions in-game as Sanjou yet. Though the musical, anthologies and anime also didn't mention them as siblings, let's wait for in-game interactions. (since, you know, we also still don't have any interactions of the Sadamune swords at all, and there's the Aoe too... what's their relationship, exactly???)