There's not a lot to talk about with this one. It's based on a four-panel gag manga and it couldn't be making that more obvious. It never has a storyline. It's basically just five hours of manzai comedy with Sonya and Yasuna, with occasional appearances from Agiri when the show feels like adding a third character.
I sort of enjoyed it. Sometimes it made me laugh. However those occasions were pretty sporadic and I didn't find it funny often enough to call it a successful comedy. I don't think it's really for me.
So... let's define "manzai".
Manzai is a stand-up act involving a boke and a tsukkomi. "Boke" (two syllables, short "o") is related to the word for senility and is the goofball who keeps saying or doing stupid things. (This isn't always because he's a moron, though. Sometimes he's trying to be a smart-arse.) Meanwhile the "tsukkomi" is the long-suffering partner who has funny reactions to the boke's idiocy.
Here, the tsukkomi is Sonya, a schoolgirl assassin. She's grumpy and violent, but she seems to get stuck with Yasuna all the time whether she likes it or not.
Yasuna is the boke, of course. She's always trying to tease, befriend and/or play pranks on Sonya, even though this generally results in physical injury. (This is quite a violent anime, but it's all pure slapstick.) She's a dipstick. She's got the common sense of half a centipede. She'll tell you off for incorrect use of nunchuks because you're not accidentally whacking yourself with them. She'll spend half an episode with a tin can stuck on her head, then immediately put it back on when it eventually comes off. She'll play in the snow when she's sick with a cold. She'll declare that she's doing something pointless and random, then forget what it is halfway through doing it.
Sonya and Yasuna are almost everything there is to this show. Yasuna boke-s. Sonya tsukkomi-s. This is watchable in a TV wallpaper sort of way, but not actually that funny. I'm not objecting to violence. The problem is that Yasuna and Sonya aren't very interesting characters and you don't really care what happens to them. Oh, they're okay. They're perfectly functional on a superficial, four-panel level. The show's watchable. However I wonder if this format might have worked better with five-minute episodes, not 25-minute ones.
Occasionally other characters appear. Agiri claims to be a ninja, but might equally be a cheerful and possibly stoned liar. They're spectacular lies, though. There's Unused Character, who's unhappy about being an unused character but is almost entirely unused. Finally there are rival assassins, who occasionally fail to kill Sonya. None of these people can scratch the show's slapstick comedy tone.
It's not a bad show. I watched it all. It's sort of surreal and absurdist, especially the opening credits. (The deadpan dancing end credits are awesome, incidentally.) I laughed at the rage-calming pose in ep.4 and the multiple Yasunas. If you're thinking of trying it, any episode will give you a good idea of the show as a whole, because it's all basically the same. Personally, though, I don't think there's enough here to justify seeking it out. The show's okay, but I'd struggle to give it higher praise.