sea dragon challange
tobirama senju in house of the dragon but he is not a targaryen he is the son of vaemond velaryon and a unknown woman that was a descendent of saera targaryen who he met in Volantis who was the daughter of a noble family that vaemond married but she died giving birth totobirama and the story is tobirama grew up sailing with his uncle corlys and got a reputation and people called him the sea dragon he has all his water style jutsu from his past life and chakra that people think its magic when he was a boy he fought in the stepstones and with his powers and leadership daemon gave him his own island in the step and tobirama made his own banner like how brynden tully was with his blackfish
the reason why he got the nickname the sea dragon is because of his water dragon jutsu he was considered someone to marry to rhaenyra and tobirama was actually in love with her and she was with him so when she married laenor both rhaenyra and tobirama and laenor agreed that because laenor didn't like women tobirama would secretly father their children so when he would visit kings landing he would sneak into rhaenyra room to sleep with her to get her pregnant and all three of them would pretend its laenor but when she gave birth to Jacaerys and tobirama knew he was not his because of his features to Harwin Strong he confronted her and found out about her affair and then finds out that she used him because of his power and position to help her own
also during the discussion for driftmark seat he would support his father because he knows that rhaenyra children aren't velaryons and tells rhaenyra that if they were his or laenor he would support them but they don't have velaryon blood so he won't and he was able to convince his aunt rhaenys to support him and his father only for her to betray them when she support rhaenyra and when daemon killed his father he demand justice and was denied by king viserys and then he left kings landing back to his island and took half the velaryon fleet with him and started blockading the stepstones shipping lain from westeros and he would get messages from kings landing to negotiate for peace that even rhaenys would come with her dragon to try one last time to get him to bend the knee to the iron throne before war breaks out only to refuse and when rhaenys returns to king landing viserys dies and during the war both blacks and greens try to get tobirama on their side
you can change the story as much as you want and tobirama personality this summery is just a rough draft i had and you can use the ideas i had in it or not pm me to let me know if you are interested