u/youRaMF

This post is fairly long, skip to the end for a tl;dr on how much maxing a bond actually costs if you do everything possible to minimize the cost.

I'm sure most of us have seen that chart showing some characters taking up to 3m fons to get to bond level 10. And yes, while some characters are more expensive than others, for the median price of a max level bond, you really only need to spend about half of what the chart shows.

Breaking down the difference sources of "free" bond:

Zero's life skill at level 5 gives a 5% bonus to all gifts at bond level 8 and below. This means you get a 5% boost for the first 71% of the required bond experience, for a total boost of 3.5%. I'll round this down to a 3% effective boost because there are other sources of bond experience you'll be gaining that don't receive this bonus.

The Fluff anomaly furniture gives a Fluffy Cotton every 24 hours, which is a free gift that gives 400 affinity. This means that if you claim and gift a Fluffy Cotton daily, you are effectively cutting the cost of maxing out the bond of a character by an immediate 33%, as there is a 3 item gifting limit per character per day.

Then there's City Hangouts, which require a bond level of 4 to begin doing. These give 200 affinity once per day. The easiest method is teleporting to the Swallowtail anomaly, going to the ticket desk, and immediately leaving the movie.

The last sources of affinity are from Memory Theater, those character icons you see around the map, and home interactions (some characters can't be invited to your home, so this only applies to those who can). Both the Memory Theater and home interactions give a one time bonus of 50 affinity the first time you do them, for a total of maybe 500-1000.

It takes 56k affinity to max a character. With only Zero's life skill, it would immediately cost 3.5% less if that was the only extra thing you had. I'm going to use Hotori as an example here. The base cost of maxing Hotori's bond with no bonuses is 2.1m fons.

2.1m - 3.5% (it's 3.5% because in this situation it is the ONLY source of boost, later on I will use the 3% effective boost as the calculation) = 2.02m

Next up is Fluffy Cotton. If you gifted one every day, it would immediately drop the price by 33%.

2.1m - 33% = 1.4m.

City Hangouts is next, giving a free 200 affection per day. You can only gift 3 items per character per day, for a total of 1200 per day. It would take 47 days of doing this to max out a bond. If you did hangouts every day, that would lower the time required by an entire week, effectively saving you 21 gift items, which in Hotori's case would save you 315k fons.

2.1m - 315k = 1.78m.

The last sources, memory theater and home interactions, while small, would save you about half a day of gifts. And realistically, if you're getting a bond character maxed out, you'll have done these things anyway, so it only makes sense to include them. I'll just round this to 800 affinity. That's about 30k fons saved.

The math changes slightly once you combine all these sources, but the effective total price, after utilizing all these bonuses, is approximately

2.1m - 3% effective reduction from Zero

2.1m - 33% from free Fluffy Cotton daily

2.1m - 210k from daily City Hangouts

2.1m - 30k from theater/interactions

It would take 27 days to get a character to bond level 9 with all methods combined, for a total gift price of 810k. The last level would take an additional 12 days, and would cost another 360k. After adding in the additional 30k from theater and interactions, this represents a total cost of 1.14m fons, saving you just over 45% of the original cost. Realistically, it's probably slightly more than this as you can't begin doing city hangouts until you reach bond level 4, but I'm not doing any more math.