Mister Mosquito takes place during the hot and humid days of summer. A lone mosquito is patrolling the Yamada household and takes every opportunity he can to feed on the Yamada clan. Tired of itching, Mr. and Mrs. Yamada, and their teenage daughter Rena begin hatching plans to foil their mutual flying annoyance.
The Yamada family are a semi-functional Japanese family, headed up by 46 year-old Kenichi Yamada. Mr. Yamada is a salaryman and loves watching tv and wearing his favorite tracksuit. He has Type-A blood. His wife, Kaneyo is 46 as well. She enjoys photography as a hobby (especially if it's family related) and is a bit of a pack rat. She has Type-AB blood. Lastly, there is 17 year-old Rena, who is the daughter of the family. She is a sophmore in high school and enjoys listening to progressive jazz in her free time and being upset at her parents. She has Type-B blood.
Mister Mosquito is the protagonist in this story and not much is known about him, except that he appears to be a small mosquito-like robot. He is driven by the same needs as regular mosquitos are, and like some of his biological brethren, he must store away enough blood to get him through the winter. He also has a strange fascination for Rena Yamada.
Each level has a human doing his everyday activity ( sleeping, taking a shower..etc). The player takes control of the mosquito and tries to sneak up on those poor humans to suck their blood and fill the blood meter. The mosquito can only suck blood from exposed body parts. Once Mr. Mosquito has landed on the exposed part, the player must then puncture the person's flesh and begin sucking out blood with the analog sticks. Mr. Mosquito must also pay attention to the human's heartbeat and sync his sucking to it in order to decrease his chances of being spotted and killed by his human victim.
If Mr. Mosquito is discovered by flying too close to the human's field of vision or extracting blood too quickly; a Man Vs. Mosquito boss battle game begins. The human in the room will try to disable and kill Mr. Mosquito. Mr. Mosquito has to dive-bomb suggestive, and sometimes humorously placed "relaxation points" on his attacker. If he hits enough of the relaxation points the human will RELAX and will resume their previous activity, forgetting all about Mr. Mosquito.
There are also many collectibles to be found in each level that allow for life and blood container upgrades and expansion. You can also unlock differently colored skins for your pest by quickly filling your blood container for each level and keeping your "boss" battle times low.