I've been dabbling with Ikuo in Ver 1.01 this past week, my best 2-ALL score is 398,289,650.
I scored 215 million in the first loop with a couple chain breaks, which is a bit sub-par for me (I'm aiming for 230 million). The second loop was a complete mess, I had at least 8 chain breaks. On a related note, I decided to give Ikuo a whirl in Ver 1.00's Harahara mode, and I got a score of 114,898,820 with my first credit.
I gameovered in the section right before the first midboss, but I had two careless deaths in stage 4 and one in stage 1, so I am thinking I could clear it. It is a good deal harder than 1.01's Harahara (which is also the second loop in a regular 1.01 run), but I think it's still doable. We'll see. I had previously gotten a score of about 90 million in this mode with Rafute, but I think it would be easier to clear with Ikuo or Momo than with Rafute (for me, at least). My reasoning for this is that it's easier to survive the first few stages with Rafute due to her long-duration bomb and quick speed, but it's harder to score with her, which means you have fewer lives to play with (which means it's harder to survive the later stages). In Harahara, you need every extra life you can get.