Ai to ken Camelot: Mangaka Marina Time Slip (1990)

Self-described "third-rate" mangaka Ikeda Marina is attending a birthday party for a wealthy friend, when suddenly a time-traveling dragon whisks the entire party away to Camelot in sixth-century Britain. There, Marina must help would-be king Arthur fend off civil war by extracting the sword Excalibur from its stone during the forthcoming solar eclipse. But the evil Lady Dola intends to thwart this plan and seize Camelot for herself.