Alyosha starts out with events leading to the main story. Estolakian (Estonia) assassin Alyosha, codemane Kortik, was sent to Japan to masquerade as a high school student to have a chance to kill Solessia (Russia) President (who is very intentionally drawn to look like Vladimir Pudin), who is visiting the same school because he happens to be old friends with the principal. However, the mission is called off last minute, leaving Alyosha stranded in Japan, with her commander's last order is for her to live as a normal high school student. Naturally, being raised as an assassin, she has no idea how to do that, and questions how to go on with her life. At just this moment, a classmate arrives and offers her cake, the first time she's ever had some. With newfound conviction, she decides to follow her last order and attempt to live normally... because the cake was tasty. From here, the tribulations and resulting hi-jinks of Alyosha trying to live a normal life begin. The plot is absolutely ridiculous filled with plot convenience, but you know from the beginning that it's not meant to be taken seriously, and instead laugh at it for it's excuse plot and attempts to make funny what when taken seriously usually wouldn't be.
However, around the chapter 20s, the series takes a more serious and darker approach. The author changes gears and decides to write a branching plot, and this was a mistake. As a reader, with the change in tone shifting from mostly comedic to a tense atmosphere, I had to look at it from a serious perspective. Once I did, the jokes before and in future chapters stopped being funny.
The characters were not enough to keep me invested in the later half, as none of them were particular endearing. Both Alyosha and another character, and FBI agent, aren't particularly deep. Both are extremely gifted at their craft to the point of perfection, not having any particular flaws to humanize them. They get in the most dangerous situations, but never once did I feel they are in any actual trouble after the shift. The author will narrate that they have this specific skill that gets them out of trouble, that the reader will just then learn about. It's another reason why the change in storytelling wasn't a good idea, because when the story gets serious, you're expected to feel for these characters now. However, on top of changing midway from a comedy where the characters before were in no danger to a serious one where they will be, to empathize is impossible, and those moments where "Oh no, Alyosha is in danger, but wait, she has this certain skill, so she wasn't in any danger at all" only furthers the detachment from the setting. The final chapter felt hollow because of this, even when it's intended to be very emotional.
Alyosha started off as a comedy, and about halfway changes gears to an action drama; one that wasn't to the story's benefit as a whole.