You Call That Service?, Vol. 5 (light novel) — Kisetsu Morita

One minion… Two masters?! Diplomatic relations between Japan and the Sacred Blood Empire are stabilizing, and the news has taken the vampire community by storm. Meanwhile, something strange is happening to Ryouta -- he's transforming into a minion! It turns out that Archbishop Alfoncina's prayer for his safety had some serious side effects, and they can only be cured with an herbal remedy sold exclusively in Japan. As luck would have it, the archbishop was already planning on traveling there for business, so she invites Ryouta to tag along. Needless to say, some people are none too pleased with the arrangement…