Most isekai-style shoujo stories are about girls getting sucked into alternate fantasy worlds. Far less common are ones about time-travel, and rarer still are ones about guys. This might be the only one I've seen that combines the two.
YUKARISM, by Chiaki Shiomi. First published in 2010 and first published in North America in 2014.
Yukari Kobayashi is a bestselling author of historical fiction at the tender age of 17. When his classmate and super-fan Makoto comes to his home to deliver some assignments, she discovers the secret to Yukari's success. Yukari's books are so lifelike because he's drawing from his own past memories as a Edo-era oiran. The more Yukari draws on his past, the more the boundaries between the present and past blur. Stranger still, Yukari starts recognizing other figures from his current life in the past, and they all seem to be connected to a mysterious fire that killed his past self hundreds of years ago.
I think what makes Yukarism truly effective is not in how it combines shoujo tropes to create a new story, but in how Shiomi creates and maintains this wonderfully understated, dreamy tone. It goes a long way towards selling the reader on this fantastical concept and keeping them captivated.
Yukari is something of a cipher, but for once it's on purpose and not because of poor writing. As someone who can drift readily between the past and the present, it makes sense for him to be so spacey from it that he ends up skipping school for days at a time and barely speaks to anyone unless forced to. It also makes him a good foil to Makoto, who tends to be the anxious sort even when she's not face-to-face with her crush. It also makes him a good contrast to his past self, Yumurasaki, who is herself smooth, seductive, and witty. The closest this series gets to comedy is when Yukari astrally projects himself into Yumurasaki and has to come to grips with moving and behaving like a woman. Luckily, Yukari is a quick study and doesn't object in the slightest to his time-travelling genderswap so we don't see any cheap jokes about having a woman's body or exploiting his past self for the sake of fanservice. He's largely content to let the forces that be take control of his consciousness and simply see what happens.
That's not to say that the story is nothing but wacky hijinxs in ye olde Edo. Just as Yukari is ready to write off Makoto as just another fan, he spots a burn-like birthmark on her arm and he starts to make connections between the people in his past and present lives. From this point on, he starts to engage with the present world actively. He starts exploring the mysteries of Yumurasaki's death and find others that are seemingly reincarnated from her time. He's even able to use his powers of observation to help a stranger get over the anxieties carried over from her time as Yumurasaki's serving girl. The irony of this situation is not lost on the reader: the more that Yukari finds himself drawn into the past, the more reason he has to engage with the present.
That's all well said and good, but what ties these altogether is the atmosphere Shiomi cultivates. Like Yukari himself, the story feels like it too is drifting somewhere in time. It's never laid on too thick, but it helps to immerse the reader and experience the story much as Yukari does. It's the perfect finishing touch for what is shaping up to a be an excellent start to an intriguing story.
Shiomi's art is much more conventional here than her storytelling. The characters are all handsome, lanky, and angular, although their most distinguishing feature are their weirdly square eyes. Interestingly, there's not a super-strong physical resemblance between Yukari and Yumurasaki so Shiomi sells the idea of their being connected through their movements and expressions. It's not a flashy touch, but it's enough to subconsciously sell the reader on the idea. She lends a fair bit of beauty to Yumurasaki's world, so much so that the modern one seems plainer in comparison. Even the expressions of others seem more muted in the modern day and I wonder if this was done on purpose or merely by happy accident. She even helps reinforce the off-kilter mood of the story through a lot of floaty, diagonal angles in the panels.
Yukarism is a atmospheric little shoujo story with an interesting story and above-average art. I'm genuinely curious to see how this blend of past and present will end and I highly encourage others to get lost within its pages.
This series is published by Viz. This series is complete in Japan with 4 volumes available. All 4 have been published and are currently in print.