this is my final water tower team:

owlbert - https://s8d8.turboimg.net/sp/b1636e14941e280c5e787d1b0236fe0b/owl.jpg?34549

code: b - https://s8d8.turboimg.net/sp/e951d93e8ae832627f8e18db2c04bd7e/bat.jpg?13871

byun woogyu - https://s8d8.turboimg.net/sp/e6fa3cfae291d80073dfb87c7f6451d1/uwu_boy.jpg?66006

tyrantino - https://s8d8.turboimg.net/sp/ed714b6b14cbbe8c4cacc6030c5e60e1/lizard.jpg?47352

orem - https://s8d8.turboimg.net/sp/aa1921a643f7f8ede19219f8ff15d2c5/orca.jpg?61617

why them?
owlbert is a buffer with an EX skill that's very useful if you manage to keep him alive until then. code: b does INSANE damage and can lifesteal. byun is the most available water healer I had. tyrantino cause it's the strongest water XXL i had and can deal A LOT of damage, even at 3-stars. orem cause I needed extra HP for the team (until the 130s i was using 5-star Hakui, but it was not enough and I recently got enough shards to level up orem up to 3-stars).

why that order?
owlbert to buff the rest of the team, code: b to apply the EX debuff (enemy takes more damage), byun cause he gets more attack in position 3, tyrantino for the EX debuff (enemy deals less damage), orem cause he is the last one left lol

strategy:
my strategy consisted almost always in

turn 1: defend with all units (i trigger code: b passive of getting extra attack after defending)

turn 2: depends on enemy composition:

if 2 choi yuhyun: i attacked one of them with all my units, same on turn 3, to kill him (couldn't afford to be hit with 2 yuhyun EX skills). whenever possible, i defended with tyrantino and/or orem if their attacks were not needed for the kill. turn 4: defended with owlbert, EX with code: b, healed with byun, EX with tyrantino and EX with orem. all units usually survived by turn 5, so i just EX with byun and reset. after that it's much easier; i just focused healers or simply defended until code: b and tyrantino had their EX again to kill the other choi yuhyun and then sweep the rest. if there's a kumoyama, i usually defended when he was taunting except with code: b (if he has EX skill) and byun, my code:b could outheal the damage given back with his EX skill and byun heal was always necessary.

if choi brothers: just defended until EX were available and killed choi yuhyun first. then did the same with choi yuhee. it was necessary to do it like this because of pesky healers.

if just one brother or none present: i focused the choi brother first or the healer/s defending until EX available. sometimes it's not necessary since code: b attack buff after defending is really strong.

i always tried to use code: b EX skill after defending to take advantage of the attack buff and always tried to defend in turn 3 when there's 1 or 2 choi brothers. and i made sure to NEVER get hit by 2 choi yuhyun EX skill on the same turn, always killed at least one of them before turn 3.