No, no character in the series is autistic.
Some of autism's most physical prominent characteristics, such as repetitive behavior in their body movements/ticks, unusual sensory behavior such as constantly sniffing or touching objects, and avoidance of a certain set of sounds and textures are nowhere present in any character of the series.
No character in the series follows any of autism's behavioral traits, either. The characters don't have trouble catching onto non-verbal queues in a consistent manner, difficulty initiating conversation, or the repetitive use of a phrase they got from somewhere else.
In order for autism to be present, someone would likely show more than one of these physical or behavioral traits, and they simply just do not. Just because a character might have awkward dialogue or seem strange in social situation doesn't mean they are mentally handicapped. It just means someone did a poor job of writing or it didn't translate perfectly well from Japanese to English.