Serious autistic nerds, Thanatoses are reserved, quiet, and taciturn, very resilient, have a very strong moral fiber, and devote themselves wholly to whatever they feel is their duty. Despite stereotypes, though, they are not very introspective, and often don't know what their own feelings are, sometimes even ending up surprised by their own reactions. They tend to have a temper and to be quick to judge others, but they judge themselves most of all, and often have running commentary of their own failings playing constantly in their minds. They tend to be easy to fluster and embarrass, but they don't like letting their feelings get in the way of getting shit done. In other words, they are a typical tsundere. They're universally bisexual but often repressed, and they can be mono or poly. As they grow older/more mature they acquire a substantial dose of chill and become much more able to understand and accept themselves.

They will occasionally have Hypnos as a twin or younger brother or close friend, and occasionally a Nyx as a parent. They don't have strict magic or setting requirements but they will often have powers/abilities themed around death, cold, and knives/blades when those are available. In settings where this makes sense, they are exceptional swordsmen, and great at battlefield tactics.

If they share a world with Azem and/or Yvette, they will meet and have an outsized impact on each other's lives. This often means romance, but it can also be strong companionship/friendship/family or strong enmity/rivalry.

They're based on the roguelite video game Hades's Thanatos, and as such that instance is their most central one, but other circumstance alts that are very natural to them are Guiding Hazard's Lee Tae-gun, ASOIAF's Ned Stark, and Trigun Stampede's Nai.

Good threads/continuities to be introduced to the character are Guide, Gunsmoke, Ice and Fire, Sanguine Blossom, Curtain, and Yggdrasil.