Suggest me books similar to the writing style of Uketsu’s “Strange Pictures” and “Strange Houses”

Hello! I am a literature PhD and my long-term partner is an ESL adult. He struggles to read for pleasure his whole life. For years, I've been trying to get him to read for fun so we can share my favourite hobby together 😛, but I have a hard time finding books with language that's suitable for his reading level (that aren't for children). Right now, his leisure reading material consists of manga and news articles, which is obviously fine, but I know he's been trying to get into reading something more substantial and most of the books I have at home as well as books we find at the store/library don't seem to hold his interest for very long or take him like a year to finish.

Recently, I borrowed an ebook of Uketsu's "Strange Pictures" and "Strange Houses" from our local library and my partner binged them in 4 days (!!). The books are translated from Japanese and the writing style is quite simple, with some pictures interspersed throughout, so that helped him stay engaged. While the reading level was probably middle school aged, the themes were quite mature. Does anyone have any recommendations for similar books (at this reading level and with mature themes, ideally mysteries and thrillers) so I can suggest other texts that will help him develop a love for reading?