Blood Type Guide
Actually you can’t increase it only if you find that same type and it’s a higher percentage, unless there’s something later in the game to perverse it.
In order for the blood quality to go up you must consume a better quality than what you have now. If it’s at 8% you need to consume blood at 9% and higher. If you consume at 8% it stays at 8% and if you consume lower it goes down to whatever that number was.
You’ll notice quickly that the passive itself doesn’t matter too much unless you’re doing a specific activity. You can pretty much just suck the blood out of whatever you need to keep the blood pool high then if you need a specific stat you can just search for the blood type you require. Just never let yourself become frail. It just isn’t worth it at all for the small hp recovery you can get from consuming hearts or rats.
To add to that even if you find high % enemies don’t feed in battle, that situation can get rather lethal, been that greedy a few times.