Sentimental Komuro Michael Sakamoto Dada-sensei (センチメンタル小室マイケル坂本ダダ先生) (or simply Masada, or Seccom Masada) is a character found in Madotsuki's dreams. He is popular with fans. He is found by sleeping in any one of a number of beds found in the dream world, going down the staircase, walking past the elevator, and using either the Umbrella or Yuki-onna effect to extinguish the fire.
Appearance
Masada is a seemingly male NPC who appears to be wearing a black suit or jumpsuit. He has pale skin and medium-length black hair, and his eyes point in two different directions (from a front view, his left eye is pointing up, and his right eye is pointing down.)
Description
The Yume Nikki thread on 2ch gave him the name, "Sentimental Komuro Maikeru (Michael) Sakamoto Dada-sensei" or "Sekomu Masada-sensei" (セコムマサダ先生) for short, as a combination of "Sentimental," Komuro Tetsuya, Michael Jackson, Sakamoto Ryuuichi, and Dada, one of Ultraman's many enemies . "Seccom" is a result of an English-langage simplification of "Sekomu."
He is found in a monochromatic spaceship, apparently the pilot. He stands next to a piano. When Madotsuki interacts with him, he makes a trilling noise, similar to the sound Super Mario makes when he loses a life. When interacting with him during the Spaceship crash event he will make a panicked higher-pitched sound. When the ship lands on Mars, his 'voice' is much more low-pitched, possibly expressing remorse or relief.
Masada is one of only two characters who walk backwards in the game (the other one being Dave Spector), who does this 'moonwalk' when the Knife effect is equipped. This is the origin of the Michael Jackson in his name, due to his imitation of Michael Jackson's iconic dance move and the similarity of appearance Masada bears to the entertainer.
Fan Speculation
Piano Teacher
Seccom Masada's usual interpretation is that he is Madotsuki's (possibly former) piano teacher. It has also been interpreted that Masada might have been a drug user, and the crashing of his UFO was meant to represent his 'crash' (Overdose, possibly his death as well).
There has been speculation that Madotsuki had lived and slept in Masada's flat outside the dream world (represented as an UFO in her dream) for some period of time, this could suggest that Masada is an adult that she trusted before she became a shut-in for some reason. Their relationship seems to be platonic, it could be that Madotsuki had a brief feelings for Masada before, but didn't know her feelings towards him (in which he speaks an alien language). However, the siren could represent police sirens on their way to arrest Masada as the authorities suspected that he was having a nonconsenting relationship with Madotsuki due to her being a young teenager.
Some fans also speculate that Masada's eyes are the way they are due to him having Hypertropia, and Madotsuki may have it too since her eyes are always closed. Which increases the theory of their relationship.
Also, the UFO where Masada lives in is simplistic and spartan, with only the big piano looking control and a table with two chairs only, could suggest that Masada is a struggling pianist who earns side income from private piano lessons.
Death
Many fans speculate Masada was a drug user, and may have died from a "crash", or overdose. This is represented when the alien ship crashes on the alien planet.
Another rumor is that he may have died in a train accident. This is shown when going down into underground Mars; the flights of stairs there are similar to those of a subway station. It is also underground, like many subway stations. At the bottom is a large pile of what seems to be train wreckage, with a figure (Mars-san) crying next to it. Mars-san could represent the people who mourned over Masada's death, and the wreckage itself could point to death by a train wreck. The fact that sad music plays during it only boosts this. Also interacting with Mars-san results in a small 3 note piano song playing. This could be one of the mourners telling what happened, a story about Masada, or just mourning.