Essentially this is a love story mixed up with adventure and some fights. Its a little bit different from what Ive already read from Kaori Ozaki. Meteor Methuselah looks like an attempt on shounen territory but without abandon the theme of love that generally accompanies the author throughout her other works. The protagonist Rain deals with the fact hes unable to die. Hes 620 years old. The behavior from him is not we would expect though. Rain is very relaxed about it. He chooses to embrace his situation even though he has experienced the loss of people he loved in the past. When Rain encounters Machika in the beginning as an enemy they start their path towards a love story. Machika is the active type of character which balances well with Rain laziness. Shes strong decided. The lovable aspect of her is that we can see her development much more than the other characters. Shes 14 so a teenager. Its possible to see her childish thoughts towards Rain. Kaori Ozaki didnt treat her as an adult as much shounen does when we have a character that should be 14 or 15. Still they have these fully developed bodies and mind turning them into an ageless character consequently stealing a little bit of their identity. Machika is a teenager and we can tell that either in her behavior as in her body. Shes so small compared to Rain that its weird to imagine them as a couple. It looks wrong. I think the author nailed in that regard. Different from other works of her the main couple is not evenly matched in their age. Shes 14 years old with an adult boyfriend. In the end I rationalized that in the past in many cultures this was the age when women were considered adults so in the context of the manga should be acceptable. However in the modern world this is too much so for me it was impossible not to find that weird to the end. Things got complicated as she starts to mature only in her mindset aspect since the whole story happens in more or less one year. As the story goes on she turns more into a partner for Rain rather than some child hes taking care of. On the other side we see Rain been more human less the immortal and wise being beyond our comprehension. So its a great dynamic between them where the more Machika grows the more of Rains weakness we see. The entrance of the third main character turns things more interesting. Yuca starts as an enemy the antagonist of the story. The natural threat that needs to be defeated or solved by the main characters but as some events happen his role in the story changes significantly and so he ends up being the third part in the RainMachika dynamic. Sorry for being vague about him but since Yuca appears only midway through the series its difficult to talk about him without giving major spoilers. Only knows that Yucas presence helps Meteor Methuselah goes past the average shounen story. We dont have a clear antagonist some force to be destroyed for the sake of humanity. Its a story where characters interaction is way more important than the big events that happen which is a characteristic of the genre.