This page refers to the adult, Osomatsu-San version of Todomatsu. Click here for the Osomatsu-Kun version, where the Matsuno sextuplets are 10-year-old fifth graders instead of NEETs.
Todomatsu Matsuno is the sixth and youngest son of the Matsuno Family.
Similar to Canon!Matsu, he comes across as the cutest baby brother who knows how to understand and win over girls. Everyone seems to think of him as a heartless two-faced brat... From there, however, he diverts.
Even as he is a reincarnation of Satan, he still claims to have a heart, and that he's only following what his script tells him to. He's not always two-faced; he's shown that he cares about everybody in The Place, and from that, believes that anyone's contribution matters.
To learn more about the Osomatsu-San timeline, just watch the anime. There are around 25 canonical episodes, along with a few bonus ones, such as Episode 3.5, which you can find in the above link, along with Episode 26 (which has been rewritten under Osomatsu's request).