 If you liked
Bakumatsu Kikansetsu Irohanihoheto
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 ...then you might like
Darker than Black: Kuro no Keiyakusha
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Both have a similar atmosphere to them. Also, Akidzuki and Hei are kinda similar in attitude and in discipline. Bakumatsu is deeply based in the history of Japan during the Edo period. So if you don't mind watching a few historical events, then you might like Bakumatsu as well.