Character Development: In the start of the series he was aloof, uncaring, aggressive, and hated the thought of working under a lord/being a Sanada's Brave. By the end, while not necessarily nice, he's far more gentle and calm, and openly admits liking being a Brave. Kakei even lampshades it when they were drinking in Jinpachi's ship, noting that he has become more gentle.
Chick Magnet: Though he attracts not only chicks. Look below.
Curb-Stomp Battle: Receives THREE from Hanzo, and another one from Sasuke in their second fight. Gives one to Kamanosuke.
Worf Effect: He's thrashed around by Hanzo in his three battles with the man, and by Sasuke during his "second fight" with him.
Worf Had The Flu: During his second fight with Sasuke, he was thrashed mostly because was having a Heroic BSOD for failing to protect Isanami. Sasuke himself was only punching Saizo to get him out of it.
Crouching Moron, Hidden Badass: Strongly implied. He never really fights in the series, and the closest to one is when Masamune forces him to duel. Masamune is using a real katana, while the only "weapon" he has is his fan. Still, he holds his own quite easily, even blocking one strike with his sandals, but decides to throw the fight soon after, laughing all the way.
Obfuscating Stupidity: It's clear that he knows more than he lets on, that he's more powerful than it seems, and his cheerful persona is just a masquerade. Saizo openly criticizes him for it, but he just laughs it off. He's basically the Kisuke Urahara of the series.
Even the Guys Want Him: It is made clear many times that men and women alike find him extremely attractive. Jinpachi's crew of pirates make it quite obvious that they would like him to get black out drunk.
Berserk Button: Getting peeked in bath, of course. Not really, her real one is family. Due to her Dark and Troubled Past, Ana seriously hated the concept of 'family' and hanging around with the Braves pissed her to no end, it's surprising that she managed to keep that Cool Big Sis facade until her time of betrayal.
Dark and Troubled Past: She was a Russian little girl who got stuck in Japan, seeing her parents dead in the middle of snowstorm. Then the family heirloom got stolen by Hanzou and being taught with many dark teachings made Ana a real cold kunoichi.
Forced Into Evil: Zig-zagged. At first, Ana really was forced to do nefarious things by Hanzou against her will because that's the only way to retrieve her family heirloom. His dark teachings, however, influenced her enough that Ana didn't feel forced in being evil. However, Jinpachi can still sense she still feels kind of forced deep down.
Heel-Face Turn: The only one of Hanzou's five to be spared (because the one who fought her has hots on her), and once she learns that the heirloom that Hanzou used to make her do his biddings was fake, she was ready to let Jinpachi kill her, but eventually accepts to become his companion.
Badass and Child Duo: He and Benmaru are seen often together, with the latter usually riding in the former's shoulder, and while Benmaru is a capable fighter, Seikai is usually the one that does most of the damage.
Only In It For The Hottie: Agreed to help Juuzou and eventually join Yukimura so that he could meet a certain big-busted blonde. And it's true. Once he's gets to know and is done redeeming Anastasia, he just stops sticking with the Braves.
Lightning Bruiser: Hits really hard. Takes a point-blank Shunko and survives. Is so fast that Saizo and Kamanosuke had trouble keeping up with him. Basically,the only reason he's not a God-Mode Sue / Villain Sue is that he was beaten one time, and because he died because of his own dumbness.