The first possibility that occurred to Angel was that "The World" Klein had offered his knowledge to Mr. Fool in exchange for some measure of assistance, perhaps even becoming his blessed and gaining privileges above those of ordinary Tarot Club members.
But a moment later, she rejected that possibility herself.
According to the timeline, when Mr. Fool had asked Angel, Audrey, and Alger, the founding members of the Tarot Club, to collect diary entries, Klein had not even joined the Tarot Club. At that point, he had only just become a Beyonder with the Nighthawks' help—a Sequence 9 Seer.
Moreover, judging by this being's response when she had recommended Klein to Mr. Fool back in Tingen, Klein had probably become a believer of the Fool during the period after he faked his death and traveled to Backlund. By then, everyone had already offered Mr. Fool quite a few diary entries, and he had clearly been able to read Chinese!
Angel then turned her suspicions toward the Third Transmigrator Klein had described. After Roselle and Klein, this was another Beyonder who had emerged from one of the "cocoons" he had mentioned, and their identity remained unknown.
Unfortunately, even Klein himself doesn't think Mr. Fool is his roommate. Otherwise, he wouldn't have suspected me... That also means he doesn't find Mr. Fool's ability to understand Chinese particularly inexplicable...
Of course, if Angel had left her brains outside the gray fog and pieced all the clues together on intuition alone, she would have arrived at an answer that explained most of these questions: Klein was the Fool. But she immediately cast that almost absurdly convenient conclusion aside, refusing to consider it.
Otherwise, Klein could not possibly have stood by and watched Old Neil, who had helped him so much, die after being corrupted