I dont think senku and kohaku would be the best choice for senku in the end. If anyone I think Gen Asagiri would be a Better romantic partner for senku in many ways. Gen isnt very secure he actually seems a bit insecure at times, when he was beat in poker he took it quite hard and acted impulsively and very dangerously to try and make himself feel better, i think senkus blunt honesty and straight forwardness is refreshing for him because he doesnt have to second guess if hes wanted. Around gen senku can be more like a kid, we see the scene of them together at the start of seasomn2 where they are in a hut together, senku planning and gen making wire, gen is enthusiastically singing senkus praises and telling the story of senkus depertification (which I assume senku told gen) to the kids and senku makes exasperated comments at gen for slacking but the fact that senku is there is interesting, gen is making wire with the kids and supervising, senku is doing his own thing but hes not in the observatory or in his lab, hes watching the kids with gen. Its also stated that senku plays with them occasionally in the manga awh. Senku can be a bit ridiculous with gen and gen will return the energy, I think gen can tell how stressed senku must be sometimes, actually gen says it blatantly, that he hopes Lillian's singing helps relieve the guilt senku feels for dragging everyone into the stone wars, forcing senku to acknowledge it. He also knows senku is not one to be coddled though

I think Gen is better for senku, Kohaku may protect his physical body but Gen protects his mind, I think senku should be with someone who understands his mind. Gen doesnt see senku as a leader or a hero like others do, he sees senku and speaks of him very fondly "senku-chan" "my dear senku". Gen does 2 things he hates, maths and physical work to build the observatory for senkus birthday. Gen openly acknowledged senkus guilt for bringing everyone into the mess with tsukasa and tells him he basically shouldnt be guilty. I think its interesting to note that I think senku much pefers gens more unmasked side like less the fake cute act he does and more the mildly cruel mischievous side of gen, when gen acts fake and cute, pouting and whining senku responds bluntly or exasperated. When gen acts naturally senku literally lights up, they are both a bit arrogant and cruel and mischievous and they are comfortable to be like that together.

I think gen is more hooked at first but we very quickly see how fond he becomes of senku at the end of season 1 with the observatory, gen admits many times he cannot do maths for the life of him and he hates physical work but yet in season 1, early into their relationship he has the observatory built for senku and interestingly enough, the song "thousands of years may have passed" which is a song that plays for taiju talking about his love interest yuzuriha and luna confessing her love to senku, it also plays in this scene for gen and senku as gen explains the observatory. In season 2 gen adopts the nickname "my dear senku" probably alluding to the Japanese dub "Senku-chan" and senkus blind trust in gen in season 4 never wavered, trusting him with some of the most important tasks in that season including knowing excatly what he was gonna do with Xeno, trusting him to watch Xeno, even though chrome pointed out the lack of communication senku only acted when gen came over and pointed it out, when senku was making fireworks gen eavesdropped and organised for everyone to gather to watch them, senku must've known gen wouldve known without telling him since he never made plans for everyone to gather together but he still showed up to do the fireworks Gen isnt very secure he actually seems a bit insecure at times, when he was beat in poker he took it quite hard and acted impulsively and very dangerously to try and make himself feel better, i think senkus blunt honesty and straight forwardness is refreshing for him because he doesnt have to second guess if hes wanted. Around gen senku can be more like a kid, we see the scene of them together at the start of seasomn2 where they are in a hut together, senku planning and gen making wire, gen is enthusiastically singing senkus praises and telling the story of senkus depertification (which I assume senku told gen) to the kids and senku makes exasperated comments at gen for slacking but the fact that senku is there is interesting, gen is making wire with the kids and supervising, senku is doing his own thing but hes not in the observatory or in his lab, hes watching the kids with gen. Its also stated that senku plays with them occasionally in the manga awh. Senku can be a bit ridiculous with gen and gen will return the energy, I think gen can tell how stressed senku must be sometimes, actually gen says it blatantly, that he hopes Lillian's singing helps relieve the guilt senku feels for dragging everyone into the stone wars, forcing senku to acknowledge it. He also knows senku is not one to be coddled though I wish we saw them in the time skip, something interesting to me is i wanna know how living arrangements were during and after season 4. In season 1 gen lives with senku and chrome in the observatory, we see gen sleeping next to senku twice, once is when ruri and senku are together snd shes telling senku the 100 twles and gen brings tea and then falls asleep on the ground next to senku, I do wonder why he showed up in the first place and then stayed and then stayed long enough to fall asleep. The second time is both of them falling asleep in the observatory while working, gens on the ground so I assume he fell asleep first and senkus sitting up sleeping as well. Then when they all moved to the stone empire area to build the ship in thr light novels its comfimed they continue to live together (a scene of senku running off and yelling to gen that they should get back to their hut and sleep or something) and senku combines their "bank acocunts" to combine their money so that he can make gen do all theur taxes, we know everyone slept and lived closely during season 3 but im interested in how senku and gen lived after the modern world was back, gens a travelling diplomat now but the last time senku lived somewhere it was with byakuya who was gone now, he then lived with gen for 2 years give or take maybe even more. I think gen wouldn't break down bht more off handedly let a self decaprting comment slip and senku woukd instantly tell him hes being stupid or Illogical and that gen has proven himself in many ways or some shit

Gut isnt a logical argument, thats not proof or evidence of anything except personal opinion

The banter does immediately equal romance but it equals chemistry. Everything else is where I can get the romance from