Mamoru Urakawa (浦川まもる Urakawa Mamoru) is a character from Mega Man Battle Network 3. Like Hub Hikari, Mamoru has the heart condition known as HBD. He has been hospitalized since he was three years old, and remarkably survives what most people would not. He is the operator of Serenade.EXE, the UnderKing and current ruler of the Undernet. He is the son of Kimie Urakawa, owner of Yoka Inn, and the nephew of Tamako Shiraizumi. 
Mamoru has deep-black eyes and brown hair, and wears a yellow long-sleeved shirt with tints of orange running down his collar into the bottom at the middle and at the sleeves, yellow pajamas with orange edges at the ankle portions, brown slippers with green straps, as well as white socks.
Mamoru tends to be secretive for the most part and for this reason not much is known about him. Despite his shy nature however, he is actually a friendly individual who gets along with people in his own age group almost effortlessly; he quickly bonds with Lan on their first meeting, and it is heavily hinted in one of the late-game cutscenes he has also befriended Lan's other companions in a similar manner. On a few occasions though Mamoru can be prone to pessimism, prompting Lan to narrate Hub's own experiences with HBD as a form of encouragement at one point. After he cured of his disease however Mamoru's disposition changes for the better, to the extent he has slightly taken on an outgoing personality as seen in various scenes on the end-game credits.
In many aspects, Mamoru is a more-than-meets-the-eye character in the series. An example of this is his frail condition on account of his HBD being countered by his status as the Undernet's administrator.
Yai falls down the loser chute following her defeat in the N1 Grand Prix, suffering a grievous head injury in the process. She ends up being sent to the Seaside Hospital for recovery, where she is soon visited by Lan, Mayl and Dex. After swearing to "sue Sunayama for all he's got!" due to the incident, Yai complains of the boredom she is experiencing brought about by the length of her stay in the hospital and imperatively orders Lan to fetch some tea for her. Lan begrudgingly agrees to do so and sets off downstairs.
At the hospital lobby, a nurse approaches Lan and inquires as to the whereabouts of a wheelchair-bound patient named Mamoru. He denies having knowledge thereof but promises to search for him, putting Yai's request behind for the meantime. Not long after Lan heads outside and finds Mamoru at the beach, with the two making fast friends with each other. Their first meeting is cut short however when Mamoru suffers an HBD strike, forcing Lan to return inside the hospital to seek help. He is quickly sent back to his room for diagnosis, with Lan trailing right behind him. Because Lan's NetNavi, MegaMan.EXE, had originally been Lan's twin brother Hub and thus had died from HBD, the NetNavi immediately recognized the symptoms upon witnessing it. Mamoru recovers and Lan promises to visit him at a later time and returns to Yai, who impatiently asks him where he has gone.
Lan visits Mamoru at the beach on their second meeting as promised. After a few exchanges, the latter yet again suffers another HBD attack. Seeing this, Lan re-enters the hospital and finds Mamoru's doctor, taking him and a nurse to assist Mamoru. This attack lands Mamoru in the emergency room, but he is against undergoing another surgery; his nurse tells Lan all three surgeries he has had previously undergone were unsuccessful. Mamoru has no hope that a fourth surgery can solve his problem, even though it is a new kind of surgery for treating HBD; upon hearing this, Lan provides Mamoru with encouragement by giving him the rare Battle Chip he wanted, IceBall M.
Mamoru's condition takes a turn for the worse three days later and he is sent to the emergency room for his fourth surgery. Three hours into the operation however the procedure is interrupted by Anetta who, disguised as a nurse, uses her NetNavi PlantMan to make the growth process of the Tree of Life malfunction and create vines throughout the hospital to render most of its facilities useless in order to find a TetraCode for Wily. After MegaMan defeats PlantMan, the Tree of Life returns to normal and Mamoru's surgery is successful.
Lan later on comes across the source of the Undernet at a hidden elevator located past the hot spring at the Ura Inn; here it is revealed that Mamoru is the Undernet's administrator, much to Lan's surprise. Mamoru then explains his father's involvement in the Undernet's creation as well as the "Giga-Freeze" program, capable of subduing Alpha but can be dangerous in the wrong hands. Not long after this the two receive word that the SciLab has been infiltrated by none other than DrillMan.EXE, who after stealing Alpha therein escapes via a distorted portal he himself had just created into the Undernet. Lan leaves to tend to the situation and Mamoru stays behind to oversee his duties as the Undernet's administrator towards resolving the crisis.
In the recent wake of MegaMan's apparent demise after the latter destroyed Alpha, Mamoru comforts Lan at the Seaside Beach together with Mayl, Yai, Sean, Dex and Chaud, expressing gratitude for the latter's companionship which in turn provided him courage towards confronting his HBD. He returns to Yoka after this but it is now assured he has been cured of his long-standing disease. A scene in the end credits further supports this which shows Lan giving Mamoru a PET, suggesting that he was well enough to NetBattle.
Despite his importance in both Mega Man Battle Network 3 and the Undernet, Mamoru did not appear in any games later installments although an e-reader card for the Japanese version of Mega Man Battle Network 6 called Mamoru's Get Well Gift (which gives the player a set of sub chips) was released, implying that he continues to remain in close contact with Lan long after the events of the third game (and presumably well into the series' epilogue).
Mamoru is Japanese for "protect", and Urakawa literally means "inlet river". His surname is shortened as Ura in Japan, which can mean "reverse" or "backwards". Mamoru's full name in English literally means "(to) protect (an) inlet river", which is actually quite accurate given his status as the administrator of the Undernet and his attempts to keep it as a secret even among his friends, notably Lan. Urakawa might be also a reference to the Undernet, as in Japan it is called the "Uranet" or "Ura Internet". As the internet itself compared to a river of data, the Undernet is a flow of information underneath the main, superficial flow of information.
Urakawa is also a town in Hidaka Subprefecture, Hokkaido, Japan.
- A longstanding speculation among fans is that Serenade.EXE is Mamoru's NetNavi, since Mamoru's father created the Undernet and Mamoru has an emblem on his wheelchair very similar to that of Serenade's. This would later be indirectly confirmed by Masakazu Eguchi. 
- While not mentioned in the games, according to the Rockman.EXE no Himitsu - Official Settei Illustration Guide, Mamoru is the nephew of Tamako Shiraizumi. Mamoru's mother, Kimie Urakawa, the owner of Ura Inn, is Tamako's older sister.
- https://www.therockmanexezone.com/interviews/2018/03/21/exe-15th-ann-special-staff-discussion-part-6/ Eguchi: “I’ll leave that to everyone’s imagination… Let that be my answer please. However, I think that the person everyone is thinking of is probably correct.”