(spoilers below)
Yeah you're right about Ichigo! The only reason he kills is to silence people so Aimi doesn't know! Daigo was also really fun to write, I just wish I had the time and willpower to actually do it 😭😭
And omg PuCo artbook..... so exciting!!! I myself personally use figma for my artbook and just my usual drawing software for my comics (firealpaca). But Figma is honestly more of a UI/UX design software that I kept using to make other stuff instead since it's very convenient for me. I'd say you can use canva for your gamebook if you want efficiency and simplicity! If you want to go crazy... maybe adobe indesign or adobe illustrator LOL, it's very overkill but the option is there!