if u want to use tohsho daigongen u either have to use the demons of tokugawa set or the mikawa set if u dont she is useless
but if it comes to that every UR is weak without the needed Characters (sets) except for Tiger and the new UR Akechi Jubei (u can get her only by spending real money/kobans via event summon).
anyway date masamune + katakura kojuuro is a "okay" combo but rly depends on which class u´r using for them...since kojuuro has to be besides characters to give em 15% dmg/def as long as they life (which means best spot for here is middle while each sides have 1 character) u pretty much have to make her a tank..
masamune is most effective as cannon, why? someone here said it earlier its because of his talon skill..also u could use archer they are faster but well weaker since they only attack up to 3 as elite while cannon is hitting everyone which makes talon trigger for each one if im not mistaken.
so now u have a tank in front line and a archer/cannon which has to be behind all other troops when u rly want to pick these 2...now u need dmg...and for this part we/i have to know which units u even have....there are a lot dmg dealers which can be set with another but to get the best out of it we/i have to know what characters u have.
personally i use masamune and kojuuro too and thats why i can tell u, there are way better units to be used. Im only using these two right now because i have em on lvl40 and max evo but will change em as soon as i can
oh and also i think kojuuros buff for masamune doesnt work.. im 90% sure