Serenade.EXE, also known simply as S, is a NetNavi from Mega Man Battle Network 3. He is the king of the Undernet and is ranked 1. His operator is unknown, though many fans believe it may be Mamoru, as he has Serenade's emblem on his wheelchair and his father created the Undernet.
 In The Games
 MegaMan Battle Network 3
Serenade is first referenced when Lan and MegaMan set out to obtain the forbidden program, GigaFreeze, so they can stop Alpha if he is awakened. The pair must fight their way up the ranking system of the Undernet to find and meet S so they can obtain this program. After defeating BowlMan (in Blue) or MistMan (in White), they reference Serenade by his first name for the first time, mentioning that in order to meet him Lan and MegaMan must find and enter the Undernet server.
The pair find that an elevator to the server is located in the back of Yoka's Ura Inn behind a boulder next to the bath. When MegaMan jacks in, he finds himself in a special section of the Under Square. MegaMan then hears Serenade's voice, saying that MegaMan can only have the GigaFreeze program if he is a "chosen one", and if he is not a chosen one, he will be frozen forever. Nevertheless, MegaMan is found to be one of the chosen ones, and he is able to take the program. As he leaves, Serenade makes a comment that he is surprised to see that another Navi is able to possess it. Shortly after, MegaMan tries to use GigaFreeze and Bass is able to stop it and hold it, showing that Bass is the other chosen one.
Serenade is not actually seen until the post-game after MegaMan collects all 200 standard chips and defeats JapanMan and DarkMan. He is found at the top of the large ramp and behind a gate in Secret 3. Serenade immediately recognizes MegaMan's power for being able to defeat DarkMan and JapanMan, and tells him that the source of his power is mercy and his respect and compassion for his opponents. MegaMan and Serenade then fight, and MegaMan wins. After the fight, Serenade tells him that he has also defeated Bass, after a battle that lasted multiple days. He then gives MegaMan rank #1 and upon leaving the Secret Area and returning to Secret 3, MegaMan can partake in Serenade's Time Trials, in which he must defeat the Alpha versions of Navis from the game in a specified amount of time using only his Extra Folder. After all of the time trials are completed, MegaMan receives Serenade S (in White), or DarkAura A (in Blue).
 In The Manga
Before the start of the series, Serenade appears to Bass and questions why he uses such a brutal fighting style. Bass does not respond and instead attacks him, trying to absorb Serenade's immense power. Instead, Serenade dodges each of Bass' attacks and reflects them back at him, injuring him in the process. Serenade tells him that he did not come to fight Bass, but simply to bring him a message from Dr. Cossak. This surprises Bass, and Serenade shows him data that will allow Bass to jack out straight into Dr. Cossak's PET. Serenade tells Bass that he should try to restore the bond he once had with Cossak, and right as Bass seems like he is about to cooperate, he tricks Serenade by grabbing his hand and using Earthbreaker, claiming that he does not need anyone and his hatred is what gives him strength. This injures Bass very badly but Serenade escapes the attack alive. Bass tells him that he will defeat him one day.
Serenade approaches Chaud and ProtoMan when they enter the Undernet to train. He asks ProtoMan why he fights and if he can continue fighting regardless of how difficult his future may be. When ProtoMan tells him that he refuses to run away, Serenade give him Muramasa.
He then creates a barrier so MegaMan are unable to follow ProtoMan, claiming that he is too weak. MegaMan tries to use dark power to enter the barrier to no avail. He then resorts to using Hub Style, and he makes his way through the barrier with brute force. MegaMan then tries to attack Serenade, but he easily reflects the attack right back at MegaMan, injuring him. Serenade then tells him that although MegaMan was able to use Hub Style to defeat Bass, it would not work on him since he, too, had also defeated Bass and was truly the strongest Navi in the Undernet.
Serenade admits that he is, in fact, too strong to materialize all of his power to fight off the dark power, and he can only send small amounts of his power to the real world. This frustrates MegaMan, who tries to attack Serenade again. Serenade notices a butterfly trapped in the barrier and he attacks the barrier, defeating MegaMan in the process, in order to free it. He then decides that he will observe MegaMan to see if he really has potential to match his own power.
Serenade later contacts Mr. Famous, letting him know that he met Lan, MegaMan, Chaud, and ProtoMan. Mr. Famous asks him if they have what it takes to take on the challenge, and Serenade says that it's possible. In response, Mr. Famous tells him to protect them if that does not end up being the case.
Following up with Mr. Famous' request, Serenade later saves MegaMan from Bass and protects him and ProtoMan from Bass' Vanishing Sword. However, despite Serenade's power, the Vanishing Sword is too strong for him and he is deleted. His power is absorbed by Bass, however a remnant of Serenade's data tells MegaMan that it is unlikely MegaMan will be able to defeat Bass, who has acquired the ability to use Dark Power. Despite this, he believe that MegaMan and ProtoMan can work together to take him down.
 Nebula Arc
Colonel reveals that Serenade was his best friend and that he holds a grudge against Bass for deleting him. He claims that he is unable to trust MegaMan, as he has become more or less rivals with Bass, until he realizes that the Bass he encountered at the Netopia base is actually CosmoMan in disguise.
 Cybeast Arc
After Bass is captured by the last line of defense protecting the Cybeasts, Serenade appears before him, telling Bass to give all of his power to MegaMan, his only friend. Bass responds to Serenade, insisting that MegaMan is his enemy, as he breaks free from the defense system.
Serenade appears to be revived and he meets with Bass, after sending MegaMan back to the original cyber world. Bass asks him how long he had been watching them, to which Serenade responds that he had been watching them from the beginning of their journey. He tells Bass that he has been feeling lonely and he offers to travel with Bass to make up for MegaMan leaving, but Bass ignores him. As Bass begins to leave, Serenade follows him and offers to also fight him once in awhile, but Bass simply tells him to stop following him.
Serenade is portrayed as being an extremely powerful Navi in Battle Network 3, as he is the only other Navi (besides MegaMan) to have defeated Bass.
- Sonic Boom - When Serenade has the ability to move up or down his columns, he can reflect any attack used against him in the form of a Sonic Boom that moves down the row he is in. This include moves that do not direct affect his HP. The only times he cannot use this move is when his movement is restricted so he cannot move up or down, or when he is using Holy Shock.
- Holy Shock - Serenade stands at the front of his area and holds out his hand. Panels on MegaMan's side will flash and damage him if he is standing on them, and a gust of wind will push him back. This move also may result in panels being cracked.
- Saint Light - Serenade shoots an orb that moves in a zigzag motion across the field, similar to that of a Sparky virus. This move can hit MegaMan even if he is using Invis.
Because of Serenade's dependence on movement to use attacks like Sonic Boom, a good strategy to use against him is to limit his movement, either by cracking panels or using AreaGrabs. AreaGrabs will also help to avoid his Holy Shock attack easier.