personalitytsuzuki is interesting in that there seems to be things that either flat out cause a schism within him, or things that he fabricates. on the outside, he has a very chipper, friendly demeanor. it's debatable that a lot of the "genki"4 aspect of his personality is a persona to keep people from questioning if something's amiss, ie an alternative means of keeping people at a comfortable distance. on the other hand, there's been times it's seemed he's put up a more dour front, likely for the same purpose. evidence to this is in the first chapter, when he kicks his partner at the time into a body of water because "he heard something so stupid he kneejerked" - between behavior like that and his notoriety for slacking on the job, it's no wonder he's been unable to hold a partner down until hisoka.
what does seem concrete about his personality is his compassion for the suffering of others and a belief in protecting the innocent. he'll go to great lengths to try and save lives, even at personal risk and suffering, be it physical or otherwise.
birth & early lifewe know tsuzuki was born on february 14, 1900, in tokyo, but thus far we don't know to whom, nor the circumstances of his birth. there are speculations that perhaps hakushaku may be his father, based on the invisible man's commentary, but nothing has been confirmed in canon. there's not even a guess to who his mother may be.
not much is known about tsuzuki's early life, except that he was terribly bullied by other children. they would chase him and throw rocks at him, their reasoning being that he was a "demon." the manga depicts him as being incredibly upsetting, sitting alone and sobbing into his hands with bruises all over, but the anime depicts this slightly differently. while he's still bruised and dirty, he's able to find comfort in the fireflies that are near him.
we can presume this was the part of his life that he learned to dance and garden with his sister, ruka. otherwise, matsushita's not gone into much detail about this portion of his life.
adulthood & deathtsuzuki's adulthood ties heavily into his death. it hasn't been established how or why, but we do know that somehow tsuzuki ended up a patient in muraki yukitaka's hospital in 1918, where yukitaka kept a case file on him and his... abnormalities. yukitaka noted that tsuzuki did not eat, or sleep - but still managed to remain alive in a trance-like state, with ocassional outbursts where he would attempt suicide. yukitaka also, interestingly, noted that tsuzuki also didn't age during the time he was in the hospital.
eventually, tsuzuki did succeed at committing suicide. upon death, he was asked to become a shinigami, and has remained such for the last century.
afterlifeat the point we're at in canon, tsuzuki is still a shinigami. he typically does well at his work, mainly due to his personal investment in his cases and the support of his partner, but it's something that clearly wears on him. we get the implication in the kyoto arc that tsuzuki is not a shinigami by choice, but possibly enma's prisoner. tired of suffering (his own and others') tsuzuki summons touda to self immoliate - ie, commit suicide again, permanently. fortunately tatsumi prevents this, but... there's still the bitter knowledge that tsuzuki made the attempt.