It's pretty poor. Masaki Tsuzuki really can't write, can he? It improves in the second half, but the first episode didn't strike me as functional dramatic narrative. It's a bunch of animated scenes. I only watched this because Magical Girl Lyrical Nanoha is technically a spin-off of it, but even that reason doesn't hold water because Nanoha is just a cameo character we occasionally see in a cafe.
Triangle Heart is a trilogy of adult visual novels, i.e. erotic video games. This isn't even its first anime. Triangle Heart 2: Sazanami Joshiryou also got an OVA adaptation, but I haven't been able to find a copy and that might have been pornography anyway. This OVA, though, isn't an adaptation but a sequel. As far as I can tell, quite a lot of Nanoha characters show up in the Triangle Heart universe, but not here and in very different forms. Chrono is evil. Nanoha's older brother, Kyouya, is a sword-wielding bodyguard with a body count as long as your arm. Suzuka doesn't exist, but her older sister Shinobu does and she's a vampire. (What? When? Was that in the OVA I watched! Some vampire neck action would have perked things up no end.)
What I actually watched, though, goes as follows:
People get killed in Hong Kong. Meanwhile, in Japan, schoolgirls are in a cafe. (Nanoha's one of them. She's at the cash register and she stops two people from having a martial arts battle. She's the only character who comes alive in this episode and it makes a tiny amount of sense that she became a breakout character and spawned a new franchise. Not too much sense, though, because she's still pretty forgettable.)
People in Hong Kong talk Cantonese. There's a girls' school. A hit man takes a job in London and has some photos of his target, including a topless one.
The end. I was already regretting watching this.
This episode has more focus. It's about two bodyguards, bodyguarding. There's a punk who seems to be cosplaying as the Joker. There's more violence, but it's still not very interesting.
There's more of that cafe again, including a near-subliminal glimpse of Nanoha, while London is once again the place where international assassins gather. They do so within sight of Big Ben, just to make sure the audience knows where we are. There's even more action, blood and killing, plus an assassin who seems to have supernatural powers. This was promising, but if there's an explanation of it in ep.4, I missed it.
There's also a concert. The hit man is trying to disrupt a concert. Why? Judging by what gets played in it in ep.4, I'm going to speculate that it's because he's a music lover.
The killing seems a bit less pointless this week, because at last I've been given someone to cheer for. He's the villain. I wanted him to kill the heroes, but unfortunately he doesn't.
That's it. Don't spend too much money trying to find it.
I mentioned a concert. Fiasse Christella is a famous singer who's going to do a world tour, but someone's targeting her and she needs bodyguards. Those bodyguards like samurai swords and have a frank exchange of views with a colleague who prefers guns. (The gun nut is wrong. Swords win! In other news, penny farthings are better than racing bikes and the best train of all time was George Stephenson's Rocket. Mind you, I mock, but it's certainly true that sword fights are on average less boring to watch than shoot-outs.)
It's not bad enough to hate, but the script lacks direction. What's the point of the cafe scenes? They add a small amount of humour in what's otherwise a drearily po-faced hard-bitten professional killer story, but they have nothing to do with anything. I presume Masaki Tsuzuki just wanted to include characters from the game. I didn't care about the singer. She's an excuse for a bodyguard story and that's about it. I really didn't care about the bodyguards. The show is at its best during the fight scenes, which says it all really.
I don't think this has ever been for sale in English. It's a sequel (not an adaptation) of an erotic video game, only remembered today for its tenuous connection with a magical girl franchise that I don't think is all that great anyway. Even if you managed to dig up a copy of this, you've got better things to do than watch it.