For the first half, I’m using Super Antonio Vivaldi’s tutorial as my basis. If I get stuck in my descriptions, just go watch the video. The later steps were guided by Bearded cubing 101’s guide.
Step 1: Align All Corners
This is the obvious first step. You can easily set up two or so, but as it goes on, it can get tricky. Once you have an edge piece flipped, hold the cube face on to yourself. Do a F2 turn to move the top edge piece down, swap it left or right to a piece that works (now on the bottom), do another F2 spin and your top layer should be complete.
I place the good side on the bottom now. To do middle layer edges, you can use a 3×3 algorithm to bring a piece from the top down. Or, you could just swap a front-right edge with a top-layer edge by bringing it up, swapping out and bringing the new piece down.
For the last layer, see how many incorrectly-placed pieces you have. If it’s all, do a standard 3×3 suni alg (r, u, r’, u, r, u2, r’). Now ideally you’ll have two in places/lined up and two not. Place those incorrectly-aligned edges on F and R and use a 3x3x2 edge-swap algorithm (R2, U, R2, U, R2, U2, R2, U2, R2, U, R2, U’, R2)
Sometimes I’ll get a bar of lined-up pieces instead of adjacent. In this situation, I do a l, u’, r’, u, l’, u to make them adjacent. Then I do the edge-swap alg above.
Step 2: Reduce Center
Find one center that you want to match up. Then flip the puzzle making this your bottom. Then we do the middle layers. You’ll use the top layer here as your free face to move around the pieces as you need. I think this is mostly intuitive, just don’t destroy your other middle-layer, correctly-placed pieces. If you get stuck, don’t forget: I can take my left (or right) center corner into my front face, then take a piece from the top and swing it down to the front, thus returning that newly-misplaced center corner back. There’s another method of doing this, but I think my solution will work fine.
Step 3: Reduce Edges
This will work something like 4×4 edge reduction. We are going to maintain one corner angular integrity and not worry about the rest of the puzzle. I usually choose the front-right corner. Your goal here is to slot an opposite piece (same colors – but a small/big to a big/small), do the angle turn, then restore. Ideally, when restoring, you’ll move another, properly-colored piece into place.
The trick here is maneuvering these other pieces into position while retaining the angular cut in the front-right spot. In addition, you’ve got to make sure the piece is slotted properly – i.e. with the big chunk on the left and the small to the right.
Step 4: Solve as a 3×3
The final step is intuitive. You may have to rotate centers, you may get adjacent edges flipped, but it should work out fine unless you get the dreaded one-corner-twisted parity. I haven’t even looked into that solution.
Ys Books I & II came out on the TurboGrafx-CD in the spring of 1990 when I was 14 years old. In the near-35 years since, I’ve played almost every iteration of the franchise: on consoles, on portables, both numbered entries and side stories. I didn’t beat them all; some I abandoned, others I completed, but I simply loved returning to the world every few years. 
