2.882 out of 5 from 42 votes
One day Ralph, the king of lizards and a proud Tyranosaurus, was hunting for his next meal when a large comet struck Earth. With no idea what had happened Ralph wakes up to discover that he's trapped in the body of a high school girl named Kana in modern day Japan! Outraged at this turn of events, the grumpy T-Rex has no intention of adapting to his new circumstances. However, with Ralph causing mayhem everywhere he goes there are bound to be consequences, especially when one of his old acquaintances is intent on settling a sixty million year old grudge...
He's small, he's scaly, he's Gon! This tiny dinosaur may seem like nothing but a lazy reptile that lounges around and causes mischief, but he's also a pint-sized powerhouse filled with energy who can defend himself when the right kind of food is involved. Whether he's riding a lion like a horse, stealing fish from the mouth of a giant shark or playing house with a group of penguins, Gon manages to get into trouble on every adventure he takes.
The main reason for this recommendation is body possessing time travel (as in, time traveler possess someone from the present). There are many other similar elements in those series, but they have a different feel (well Ruka to Ita Natsu is a romance series, while Boukun Tyrano-san is a comedy with just a hint of romance in the background). Despite that I do recommend you to give those two a try.
Both of these manga are eichii with gender-bender themes. Trans Venus goes all out with the gender-bender, while Boukun Tyrano-san takes a more unusual approach (with the main character being a male T-rex who is stuck in the body of a female human). Both manga have crazy, over-the-top plots. It should be noted that Trans Venus is alot more explict than Boukun Tyrano-san. That said, I have a feeling that if you like one you will probably like the other.