Hey TGD, so my HS strategy for BotA2 turned out to be a slight variation on Hamufurai's 1055k vid (I didn't even know if Hamufurai had used the same core strat as me until some of his old MM vids were posted by kg1000 just last year). As you show in your vid, the trick is to keep Doku on the outside of the screen to be able to safely charge UTs on the ghost fish, and also on Doku himself where possible. You want to collect 8 of the 10 essence orbs with Benediction, then use the remaining two to score another UT on Doku, and repeat for this all four waves (definitely harder than it might sound!

). I use the VF for the UTs on the ghost fish because of its long active frames, which usually allows you to take out all 10 fish in one go (this has its advantages over having any fish left over in the same wave because you can better manipulate the essence for collection and follow-up UTs without the hassle of an agro'd fish chasing you around - however if you can get two UTs on the fish and one on Doku like you did in the first wave in your run, and without losing a load of health, then that's great

). So the basic strat for a score like Hamufurai's 1055k is two UTs per wave, one on the fish and one on Doku, in good time (say roughly 175-200 secs) with no items/ninpo used, maybe with an extra UT on Doku.
For say 1070k+, you need to score more UTs on Doku himself - I use the lunar for this. Using the camera-centering function (R1 on PS3/Sigma) in combination with a tactical roll away from him, you can get Doku on the edge of the screen pretty easily (as I practised more I got much better at judging the away-jump distance into OL UT after baiting a sword swipe/flurry etc.). You can make contact with a lunar UT during the active frames of his sweeping sword lunge attack and grab animation, and also in a few frames immediately after he throws his sword (standing/charging near a wall/column can often, but not always, rebound his sword and avoid hitting you, making it possible to time your UT release when he's next to you but still off-screen). The lunar obviously also allows for fairly minimal damage if only the last hit(s) of the UT make contact, say immediately after the sword throw, allowing for more UTs to be achieved. Positioning (no further away from Doku than about 1-1.5 base jumps) and release timing is important when going for UTs on Doku, otherwise he'll either block your UT or he won't reach you if he's too far away when you tap R1/recentre the camera) to get Doku back on-screen and release your UT. I found it difficult to make any extra UTs worth the time trade-off at first, but after a while it became easier. So on my 1097k run, I got 79k ET/UT points: four UTs on fish (with 8 orbs collected w/Benediction in each wave, giving ~23k essence), then four UTs on Doku with the VF using the two orbs left over in each wave, and then 8 extra lunar UTs on Doku over the whole run, which equates to about 2 per quarter of Doku's health bar (final time was ~268 secs, bit slow but a necessary consequence of setting up those extra UTs). I can remember that I missed one UT on Doku due to my own mistake with release timing, so 1100k is definitely doable, but pretty much everything would have to go perfectly which, from my experience with this mission, just doesn't happen.
Hope that's at least somewhat useful mate! This mission was one of the hardest to max-out karma-wise, really frustrating stuff and definitely one of the worst for adverse RNG. Any number of things can instantly end a run, one of the most annoying being when Doku kills a fish and then they all rush you. That's one reason why just getting all four ghost fish waves to go smoothly in a run is hard enough, let alone also farming Doku throughout

The small elixir is definitely a god-send for this mission when you inevitably lose some health (shame there's not a few more

). I also spent a long time trying to figure out how Hamufurai had 1055k and I only had 909k (getting about 3 UTs in the whole mission going for a TDS speed-kill

), then I eventually found out about safe UT charging for the fish essence

My progression on this mission was 1020k, 1028k, 1045k, 1046k, 1067k, 1097k, so definitely a very gradual score increase over time. Best of luck man! I've not played NGS for about a year now, so will have to go back to MM soon.