i just wanted to discuss what we each think about tobirama since we haven't gotten to the "meat" of who exactly he is/was. without the revelations we have a nice period to guess as well as contribute inductively to plausibilities.
tobirama certainly acts like a hot-head and usually gets that way when recalling memories of madara and other uchiha ordeals.

he seems to struggle with a nature / personality duality. i find that refreshing given that it's more complex than the usual "morally grey" character with a clear leaning. in this did he influence both sarutobi and danzo in distinctly different paths yet while he molded them so differently he was totally genuine in each attitude and ninja way.

he is an approximate see-saw of greater good and lesser evil types of choices and obviously some were to be tough calls, such as policy and relations with uchiha.

i would dare say that tobirama is more integral to madara and hashirama,s rivalry and battles.

but look at how he becomes consumed and 4th raikage level berserk! he is definately afraid of madara but it must have more to it. to have gone to the extent he did as hokage to manage the uchiha's then he must be partially "diseased" with a minor case of naruto universe's version of hatred and darkness while a will of fire burned inside. with that, there must have been a chain reaction of injustice that occurred between the 4 top brothers. whether it began with izuna's death or something else, tobirama almost certainly got his share of retaliated grief and inflicted pain. i think tobirama lost someone he loved before the hashirama + madara fight settled almost once and for all the their close quarter cycle of hatred.

izuna aside, im almost certain we will learn women were involved. who lived whom and when + who killed her and why. there were maybe two scandals, uchiha and senju fighting over mito's heart. another, tobirama took an uchiha wife and a romeo and Juliet type tragedy occured, explaining tobirama's understanding and bitterness
towards the uchiha way /curse of love.

to crazy this up, obiti could even be tobirama's grandson! when you begin to wonder about orochimaru's informal indictment of tobirama's policies then you can see how obito ultimately became a product of those policies by the indirect factors and conditions of the generation before him. it's poetic "infinite tsukiyomi" justice. also, both are space-time jutsu users. as an inherited trait, obitos sharingan may have been influenced by that ability as he awoke his first tomoe and later his mangekyo. spacetime jutsu ingredients genetically passed to obito and seeping into the "despair" chakra and heavily influencing the optic nerve. and, given the example of tobi= obito then why not throw good taste out the window and assume this name relation trick applies here! clear beef between the ramas and madara, madara would secretly keep tabs on tobirama's family and perhaps use them for his schemes ( shaped obito and nobody noticed, ala pein's false memories.