Would you believe me if I say this custom chart is doable handheld? Also flashing lights warning from the note hit effects and the background MV
Chart ID: BXM4L5BH
Chart Difficulty: 30+
Chart Song: Grave of Halo
Chart Name: Grave of Halo 4k (doable handheld)
Okay, so to explain, there are 2 things that allow for this chart to be playable handheld (by which I mean holding up your phone and not having it down on some sort of surface),
The first thing is a way of gripping your phone called a claw grip (I've attached some images in the replies so feel free to take a look as you read), this technique allows you to have additional fingers to use other than just your thumbs, which is necessary to play this chart.
Now that is not all, you may notice, a claw grip has your index fingers positioned quite high up on your screen, and nowhere near where the notes are hit, well here comes the second part, In Holodori, there's no limit to how high up you can tap on your screen, so for example, while playing a song you can actually tap at the very top of your screen to hit the notes and it'll still get registered, though keep in mind that you still need to align your fingers to where the note is meant to be hit, which is harder to do cause your fingers are so far up from the judgement line. Alright so, you can take advantage of this and use your index fingers to help hit the notes from higher up on your screen (you can see an example on image 2 in the replies), and, I actually charted the chart so the notes that you're meant to hit with index fingers are specifically only the gold notes, as a form of guide to let you know when index fingers are required.
And that should be it, it will take some getting used too, and I will add that this gripping technique does have its downsides, like I personally have a hard time moving my thumbs as swiftly as I would usually, and also it gets tiring keeping this grip for a long time, so I’d say only use this grip when necessary, and just use a more comfortable grip when playing casually.
(Edited)