I see Sukuna subscribes to the Indiana Jones school of danmaku.
@ghap: These are in the original Japanese, except with penciled notes in the margin indicating the pronunciation of some kanji (in hiragana), plus the definitions of some words (these notes are in Korean hangul). Not unlike the notes you find scribbled in English textbooks owned by ESL students, really.
Whoever owned and scanned the raw must''ve been a Korean who was learning Japanese. In any case, these scans are good enough (for reading and for translating into other languages), so anyone who's picky on 'unaltered' originals (unaltered as much as a scanned-and-edited-in-photoshop copy can be, anyway), could just erase the notes in the margin and textboxes with a simple brush tool (taking care to match the pixels in the background), unless they want to go to the trouble of buying their own 'clean' copy and scanning that.
Alternatively, a digital version of this doujin is also available for sale. That one contains 12 pages though, oddly (maybe it's more complete, but includes blank or solid color pages and/or scribbles).